Products for fine hair

I use I use Big Sexy Hair shampoo and conditioner. Then I spray on Bumble and Bumble thickening spray before blow drying, and after drying I use a little L’Oréal LockIt fine control spray lightly and kind of push the hair up at the roots. This helps it to stay fluffy throughout the day.

I find when I use a mousse or gel thickening product, it will actually weigh my hair down, so going with a spray thickening misted lightly over washed hair works best for me. And unlike most people I know, I have to wash it daily.

I like a good texturizing spray like Garnier texture tease or Oribe dry texturizing spray

Tigi Catwalk Root Boost. Spray at the roots on wet hair. I comb it through then dry my hair. Gives me serious poof.

I have fine, straight hair that lays extremely flat - especially on Day 2.

Obviously some sort of spray/mousse and a good blow out with a round brush is a must on Day 1. I think I've tried every wet root boost spray/mousse on the planet, and I haven't ever found one that is significantly different than the others on my hair.

On days I REALLY want volume, here are my two go-tos:

A root crimper similar to this -- they don't make the one I have anymore that is more like a curling iron style, but I think this is better anyway because you need to put pressure on the area you're crimping. You lift up the top layer of your hair and crimp the top inch or so of your roots. It's awesome because your hair still feels very soft, easy to run your hands through. Downsides are if your hair is thin in addition to being fine, the crimps might show through, plus if you have colored or fragile hair, obviously heat treatment isn't great for it.

Volumizing Powder - I've tried several brands on this as well but always come back to the Beyond the Zone for how well it works AND the price. Sorry, not paying $25 for a tiny bottle of the stuff that is basically powdered glue. This stuff is amazing - works right where you put it, really lasts, and can be "refreshed" and fluffed easily during the day. Downside is your hair definitely gets... weird feeling where you put it. You can't see it, and I wouldn't quite call it "sticky" because it's not wet feeling at all, but you can't run your hands through your roots easily and you need to wash your hands after you put it on/fluff it. This is my go-to for going out/events, but it's too weird feeling for my taste for daily use. For example, I have a hard time putting my sunglasses (which also have a rubber part on the inside of the arm) up on top of my head, in my hair, when I have this in.
Edit: They also make one for dark hair that I assume is dark colored. The powder is white, and my hair is nearly black, and I never have any problems with it blending right in. However, I don't have thin hair, I just have fine/flat hair, so YMMV. 

Hope this helps!