If they're all friends, it's fine, you'll get each other sometime.
If they're colleagues? If they're people who've paid for you before and don't expect it back, it sorta becomes an obligation to do the same to not be a cheapo, no?

Here's what I'm thinking. If they've gotten it for me before, I'll get it for them next time unless they seem the type of person who would pick a cheap restaurant when it's their turn and ask for an expensive place when it's yours.

If they're friends or people I meet on the reg, IDGAF.
I'm reasonably well off.

If we're new friends, I'll go halfsies unless they change the status quo or until I feel like I like them enough to offer the whole thing. I don't expect them to have to get me later, I just need to like them enough.

Thoughts?