What could I put in this fish tank?

Your tank is fully stocked as far as fish go. Fully.

You could, assuming your tank if fully cycled and well established, add a few smaller shrimp such as Red Cherry or Ghost. (Some Bettas eat shrimp. Most don't.) Or a small snail or two. That's about it.

No other good fish options

But a snail, some shrimp, or an African DWARF frog might be OK.

The tank is a bit small for other fish to live with a betta. Most of the suitable tank mates are schooling, and the tank isn't big enough for a school of fish. The other options generally get to big.

Ian

I have 5 guppies with my Betta. He doesn't bother them at all, in fact he is up at the top with them when it's feeding time. They are guppies I raised myself that turned out to be Rainbow Fantails. Their parents are Blue Turquoise fantails. Go figure. I also have 3 dwarf Cory Cats and everyone gets along great! Depending on your Betta, try a couple of what you are going to put in and see how he reacts. Have plenty of foliage in there. Fake plants are ok. Good luck

you could get one or two small community fish such as guppies, molly's or neons. I wouldn't get more than two more fish though, it's not really a big tank and you should only have 1 inch of fish per gallon.