I use a relatively large amount of black truffle and pineapples.

Pineapples are the easiest to make piety food since it's all you need and you need a lot of them. You have enough time to hit both the spruce logs and it.

Clusters still sell relatively high on my server and tier 4 materia is starting to pick up in sale speed with nobody farming it so it's still relatively high. If you were to go out and farm them for sale Fire/Water cluster probably would sell in the highest quanities since food is made in higher amounts normally.

Aside from that the rest is all more or less worthless.