Are we allowed to use amc gift cards to purchase tickets, popcorn, etc?

Yes

You can use it tu purchase anything in the theater except to give tip. Always remember to carry at least $5 in cash.

You can use gift cards for tickets, popcorn, food, and drinks. You can also use it for alcohol. There is a bar next to the video games. Make sure to have cash, you can not tip with gift card. Also, they will let you know wether you can use gift cards or not.

I think only for tickets.

Tickets yes, but I don't know about popcorn. I assume so but I am not sure