All can be tricky. If you turn the sentence around to “All I need to make the salad IS a head of lettuce and a carrot.” Because all = the only thing, even though the predicate is two things. But for sure as others noted your sentence has a plural subject and needs ARE.

Hello! It would be "are" because you are mentioning two things and therefore you need a verb that goes with the plural form. Also, I woould write the sentence differently: Lettuce and carrot are all I need to make salad. I hope to have helped you!

are all i need. so all here means = everything. as in, i need nothing more.

Some lettuce and a few carrots are all I need to make a good salad. Lettuce is an uncountable noun, therefore “some” is the quantifier used. Carrots is a countable noun, so a number of carrots or even “a carrot.” I hope this helps 🥳

"Are"