First of all, it depends on the nature of the gathering between you and your classmates. If you are having a graduation party, it is recommended to give your classmates some commemorative gifts. If you are still in school and this is just an ordinary gathering, you can bring some small snacks and other gifts, so that everyone can spend time together and increase the relationship between classmates.
Secondly, it depends on the person you are giving the gift to, whether it is a male classmate or a female classmate. For male classmates, I suggest that you bring a bottle of good wine, so that everyone can taste it when they get together. For female classmates, it depends on your financial situation. If you have sufficient funds, you can give each person a small pendant, a mobile phone chain, etc. If you have tight funds, you can bring a box of chocolates and share one piece for each person. Girls like it very much.
Finally, I will give you another suggestion. Collect everyone's photos at the party, and then customize a photo poker on the Internet. Each poker is a photo of a classmate, and then everyone has a pair. Such a gift is very commemorative, and the price is not expensive. Classmates will not let you spend money yourself, and they will definitely "buy" their own pair in the end.