If I remember correctly, there is peanut butter and jellys in little individual servings at the buffet (like to put on a bagel or toast)...
We have a kiddo with food allergies and eating in foreign ports is just terrifying, so our carry off snacks were (all carried on to the ship) individual packages of popcorn from Trader Joes, individual servings of potato chips (and FWIW, we never saw anything other than potato chips on the ship..and they were in a large community bowl), also individual servings of Oreos, pretzels, cheese its, peanut butter ritz sandwiches and also tuna kits...we also packed bottles sodas and waters and bottled juices.
Do keep in mind that you can not take opened food off the ship OR back to the ship, so what is not finished in port, becomes trash unless it was unopened.