what to do with dupes?

i know this is a stupid question & have probably been asked before, but i genuinely don’t know what to do with the dupes that i have!

how do you guys sell them? what apps are best for selling? do you create some sort of arts and crafts with them? i have so many and i really don’t want to throw them away.

what are some things i can do to maybe sell or make with them??