Shitty shops full of random crap just like where you found the silicone covers.

[He... He did find them in one of the shops, didn't he? Did someone else find them and just hand them to the guy? Is Sanji giving Donut too much credit?]

Any DIY knowledge is going to come in handy for you, but there's no point in bargaining when there isn't anyone minding the shops.

[He waves the very idea aside. After all, there's no currency either. Bartering is as close as anyone seems to have gotten to an economy here.]

If you can make something useful with your weird ass crafts, you should be fine.