I find that there is always a lack of food on the AH on my server. I can't speak for other servers but most food is pretty easy to farm and sells for pretty big money.
I can do a loop around the terrokar basilisks along the rivers and just toss 2 dots on each and they will die. Doing this and just making a contiguous loop around the rivers I can easily farm 3-4 stacks of basilisk meat an hour (sells for 20g a stack). Between that and the grey crap they drop that sells for ~2g a stack, plus greys/greens/blues it's
easy to make over 100g an hour. These things are hardly farmed my server and even if there are people there it can easily support 3-4 or more. Also I just keep the
[Dampscale Basilisk Eye] in my bank and I keep an eye out for people who are looking for them, often by the hundreds. Kind of hard to find buyers with those but when you do they sell in quantity. These mobs can also be skinned so if you're a skinner you are making tens of gold per hour in leather alone.
I mean it's literally so easy and quick to farm that I can hop on at 7:00 and by 7:15 I can have a stack of basilisk meat for a raid and make a quick 10g in trash drops.
I don't know about the other foods but I'd assume, especially if you have a high population of raiding guilds on your server that this stuff is in high demand.
Other than that, you obviously mentioned Skettis which used to be better for farming when the elementals were on land but it's still pretty quick and you can get 6-8 primal waters per hour or more which go for 20-25g on my server.