My personal endgame recommendation to efficiently get prepared meals is to plant onions and to then cook onion rings.

This is due to the fact that you can stack up to 30 onions and that you only require 2 onions for each dish of onion rings. This means that you can cook 120 onions at once for a total of 60 onion rings. You can almost fill an improved preserving machine with just these 60 dishes as that requires 6 of 8 slots.

By doing that you will get a total of 3360 prepared meals from one batch of 60 onion rings.