Harry Potter at Universal ?

You can do the HP worlds in a day depending on how crowded it will be. We rode everything we wanted to ride but did not ride the "big" HP roller coaster. Can't remember the name..

You MUST try the butterbeers. There were three of us and we tried all of them. I enjoyed them all but loved the frozen one and I usually don't care for frozen drinks.

You also must do the wand ceremony at Olivander's. My 17 dd got picked for the ceremony and we really loved that!! She did buy a wand, too. It was kind of fun to go cast spells around the parks but probably wouldn't do that again.

My biggest tip.... minimize what you carry into this park. For more of the rides, you have to store your belongings in a locker and the locker rooms are a NIGHTMARE!!! They will accept credit cards at least. They just don't have a lot of space in them. Just let one person manage the locker situation unless you have a lot of stuff. There is just not enough room in those spaces. I almost had an anxiety attack for real. Bottom line, this would be a good day to leave the big camera at home and wear shorts with lots of pockets. I did have my big camera because I wanted those cool pics of Gringott's, etc.

It was quite a walk from the entrance of the park to the HP worlds so be sure you are wearing comfy shoes. You will also need park hoppers because there are two worlds you can visit. We didn't do anything else at Universal so it was a lot of money to spend I thought but we did enjoy it.

We took the kids there a few years ago & we all had so much fun! It's totally doable to do the 2 parks in one day.

At one of the stores, buy their HP stamps & put a postcard in the owl post to yourself. It was so cool to get these after we got home. Complete with its own special postage.

We got to the wand shop about the time everyone else did. It was beyond packed! People were waiting to be able to "find their wand". My kids chose one themselves & we left. I know it's an oxymoron to go to a park with all the people, but I hate small, crowded rooms.

I can only speak for the Gringotts ride. We loved it! It broke down a few times while we were waiting in line. We just sat where we were until they got it going again. I don't know if that's a regular thing or just one of those days.

Have fun & wear comfy shoes!

Edit it add: We didn't carry anything with us. When we were there we saw them even telling people that purses weren't allowed on rides.

No bags are allowed on Forbidden Journey or Gringotts. No items of any kind are allowed on your person, except a lanyard holding your ticket and regular glasses, are allowed on Dragon Challenge. They have metal detectors for you to walk through to check. If you are planning on doing other rides in the parks Hulk and Rip Ride Rocket are no items allowed on your person, and The Mummy and Men In Black are "no bags" ride. The lockers are free while you are riding. It will tell you how long the free period lasts when you choose a locker, but they are generous. For some reason people like to huddle next to the first locker screen they get to, when there are lots of empty screens around the corner or down a different aisle.

Butterbeer is sold at many places. In Hogsmeade the line is usually shorter inside the Hogs Head, and the two carts will have the longest lines. In Diagon Alley we normally get our fix in the Fountain of Fair Fortune.

There are two Ollivanders locations. The one at Diagon Alley will be a shorter wait because they have more rooms available.

Each side has two different entertainment shows. Hogsmeade has the Frog Choir and the Triwizard Tournament Pep Rally. Diagon Alley had Celestina Warbeck and my personal favorite, Tales of Beedle the Bard featuring the story of the Three Brothers.

Hogwarts Express is different both directions.

I prefer the food at the Three Broomsticks over the Leaky Cauldron but the Butterbeer Potted Cream at Leaky Cauldron I really like.

Oh my. Your post stresses me out! One day? Yes, you can "do it" but there is so much to see. We spent four days in the two (entire) parks. If you stay on the property, you can get an extra hour. Ride the rides using the single rider line. They generally go much faster. Butterbeer is a must.

You cannot take anything on the rides.  If you have a jacket you have to either wear it or tie it around your waist.  No purses, sunglasses, bags, etc.   
I took a very lightweight running jacket that has lots of pockets so I was able to keep my lip balm, sunglasses, a credit card and my phone in a zipper pocket.  The rest we put in the lockers.  SaveSave

No bag and some of the rides have metal detectors. When they tell you to put things in locker, they mean it. There are ride lockers next to those rides or you can get an all day one to put your stuff in.

The lines for the lockers can be long.

The rides vary with what you can take. If you can't take something on a ride, signs will let you know and you will be given free use of the lockers. We sent someone to get in line while the other one put stuff in the lockers.

I refuse to let people line jump when they do this, so be warned that the locker person may not find the rest of the group.

oh man, you want to set people off on the DiSboard, bring up this topic. HUGE hot button issue over there. I can see it working on the single rider line. and FWIW, freecharlie I agree with you.

it is just a giant pet peeve of mine. The rest of us waited in line at the locker and then the line for the ride. Why do you get to circumnavigate the process?

And most people do not do this as far as I can tell because only twice in 5 days at universal did someone try and both times they did not pass.

The Team Members instruct people to do this every time I've visited.  If people approach the line with bags.  The TM holds them, one person goes to the lockers and the other proceed into the line.  Especially at Gringotts.  When that ride first opened they even gave out tickets to make the process smoother for the person joining the line later.

You may want to do a quick look at the rest of the park to see if there are things some of your party will want to do. I enjoy most of the different areas of the parks at Universal, and our strategy for a day in the parks is to do HP until it starts to get too crowded, go do other things, and come back to HP in the evening.

1) You need park hopper to do both sides. Someone said not to ride the train, but as long as it isn't first thing in the morning, it is still faster than walking to the front of one park then to the back of the other. Plus, you need to ride once in each direction to get the whole experience.

2) The Express Pass passes now work on the HP rides. Pricey, but I would seriously consider it to maximize time. This will sound nuts, but it is probably even be cheaper to get a hotel room at one of the three resorts that offers express pass to get a day of unlimited express pass for your whole party.

3) The lockers aren't that hard to manage. DD always goes in, gets the locker, and then meets me outside the locker area. They are free to use for long enough to ride once or twice. We tried not bringing anything once, but we still ended up buying stuff during the day that had to be stored.

4) On the two big rides (Hogwarts and Gringotts), you need to do the full queue at least once. After that, you can use the single rider line if you want to re-ride. We don't mind not being seated next to each other, and we've never been more than a couple of carts apart.

5) New wands are a must. The interactive wands are fun around the park, even for adults.

6) If you want a fun souvenir, there is a photo experience where you take pictures in front of a green screen, and they turn it into a video of you at Hogwarts locations. It was pricey, but fun to do.

7) I would plan to eat one meal at The Leaky Cauldron and one at The Hogshead. I stay mesmerized the whole time I am in both.

8) The HP areas at Universal are my happy place, so I'd totally take advantage of a day.

9) This is another expensive option, but when we did Universal in CA, we found that the VIP tour was worth every penny to do everything in one day. Universal's VIP Tours are priced better than Disney's, and they hit all of the park highlights plus give you express passes for after the tour.

Right at $50. The ones without the interactive feature are a little cheaper - maybe $45.