In general, the sort of diet you should be eating depends on a few factors. Are you in hardcore, softcore, or aftercore? Do you have skills or IotMs that give you access to special consumables? How much meat are you willing to spend per adventure gained? There's a useful site here that offers suggestions on how to get the most adventures you can afford every day from consumables, although it assumes you can buy whatever you want from the mall, but it sounds like you haven't ascended yet, so your only real restriction would be what you can afford.

Milk of magnesium is a great choice because it's actually a potion, so it can be used on top of whatever you were planning to eat anyway. It gives you +1 adventure for every fullness point of food you consume while the potion's effects last. Keep in mind that the effect's duration is used up by the food, so if you only have 10 turns of the effect, eating 15 fullness worth of food will only give you +10 adventures. There's also the accordion thief buff, The Ode to Booze, which works similarly, except instead of getting it from a potion, someone needs to spend 50 MP to cast it on you.