Answer:
costs
Step-by-step explanation:
In the context, the most appropriate word would be "costs".
This is according to the subject-verb agreement. When the subject in a sentence contains two or more than two nouns or more than two pronouns and the sentence is connected by the word 'and', then we have to take a verb in its plural form.
In the given sentence, tomato slice, pickle, lettuce leaf are the nouns and they are connected by 'and' so the verb has to be plural.
Thus, 'costs' best fits in the sentence.