Veggie Stew is actually extremely nice for dungeons, since it lasts for about 12 minutes, and the effects can stack. Normally you heal about .7 health per second, and even a level 50 character will only naturally regen about 3.5 health per second naturally. Of course at that point it's pointless to use anything but really advanced healing spells/potions, but up till level 20, veggie stew, again, can be extremely nice.
For example, just before you run into a big fight you eat 4 of them. That's 2 weight. Assuming that you take damage from the beginning, you will be regenerating health at a constant 4/second, replacing a single weak healing potion every 5 seconds...if the fight lasts for longer than 20 seconds, you've already made up for the weight! If it lasts for two minutes, that's the equivalent of nearly 40 healing potions, or 20 weight, 10 weight, or 5 weight...and it's much cheaper than the potion equivalents ^.^
If you somehow manage to get yourself into a battle that lasts for the full 12 minutes, just those 4 stews will heal almost 3000 health, the equivalent of almost 60 weight worth of healing potions, all for 2 weight! Not to mention the extra 4 stamina per second you'll be getting, upping your damage significantly ^.^
So while most foods are fairly useless, some are far from it!