What do you call this kind of meal?

Pantry Surfing

On our menu plan is is "OYO" for On Your Own.

Another “Your on your own”.

We call it fend.

Fend for Yourself. With just the two of us now, it happens more often these days.

We just say "everyone is on their own" or "you are on your own."

"Catch as catch can."

Such as "it's catch as catch can tonight."

Absolutely no clue where it came from.

OYO or scrounge.

You're on your own meal

Fend for yourself if leftovers or whatever you want to throw together from the fridge. If I’m trying to clear the freezer out I call it frozen food fiesta.

We never really had a name for it.
When we were first married, it was ‘where will we go for dinner’ night, usually on Fridays. After kids, DH or i nearly always cooked a meal, though we sometimes had takeout. 
As the boys got older, they were sometimes told they had to organise their own dinner if DH and I were going out without them. Often, they would ‘find a friend’ and invite themselves to dinner there.
Now it’s just the two of us (and sometimes just me), but still one of us cooks most days. There are weeks like this week, where DH is not going to be home for dinner on two nights, where we have deliberately made enough food on a couple of nights that I will have leftovers to eat on those nights. We also plan to eat out ever couple of weeks, but that is often done in advance, not spur of the moment.

Like many others we call it fend for yourself. My go to is usually Bacon Ritz crackers and cheese or butter and noodles,, my husband is what ever packaged noodle option he keeps in his office room.

"you're on your own" or "forage"

We call it potluck.