I’ve sold at Anime Central (artist alley), C2E2, NYCC, and Megacon (exhibitor) and the art show at SDCC. I fret endlessly not just about how much stock to bring, but of what. It’s totally unpredictable. At some cons I’ll sell out completely of say fortune cookie plush the first day; so the next one I bring 30 and only sell two. It’s muy mysterioso.
I think with handmade stuff you have to assume selling out is your GOAL. Since handmade stuff is limited by necessity, that has to be your advantage over mass-production. Other than that be prepared for continued headdeskery over whether you made the right amount of the right thing X_X; Or whether someone will ask why you haven’t got any tacos.