2 gallons is considered too small for any fish per the recommendations I see, but shrimp could go in there. For bettas, the minimum recommended is 5 gallons, 10 is preferred (that's what I have), though there are some exceptions like some disabled bettas with bent spines, extra long fins, or seniors sometimes do better in a 3-ish gallon tank.
Pet stores still sell the little ones and they are labeled as FOR bettas, which kills me, but they don't care, they make a buck. Some people have their bettas in much bigger (20, even 40 gal community tanks) tanks, especially the ladies, who have shorter fins.
In a 10 you could do a school of some type of nano fish, like tetras. Even snails like mystery snails or nerite snails (Sanglainn is a nerite) get recommended 5 gallons minimum per snail, though perhaps the little guys like ramshorns might do ok in a two? I'm not sure of their minimum requirements.