To unlock the Self Sufficient trophy in Red Dead Redemption 2 you need to craft thirty unique items. You can craft most items at your campsite, which you can set up out in the wild at any time by selecting the camp from the bottom of your Items wheel.
Variations on items count as unique, so you can make up numbers by crafting different variants of bullets, cook meats with different seasonings etc. Horse and human tonics count as well.
It also appears that crafting legendary trinkets at the Trapper and crafting pouch upgrades with Pearson count towards your 30.