Counting problems often happen in stages. In the tree diagram, choosing a wrap is one stage and choosing a drink is another.

An option is one possible choice at a single stage, and an outcome is one complete result after all stages are chosen. Each full path on the tree is one lunch outcome.

If every first-stage option can go with every second-stage option, use the product rule. For two stages with $a$ options and $b$ options, total outcomes are $a\times b$, so here $2\times 3=6$.