It’s an odd combination, but I’d like to start with the foods that are either least filling or least available- namely, the non-meat foods.
Perhaps the easiest food there is is the apple. An apple will fill two meat-sticks (or meat-pops, depending on who you ask) of your hunger bar, and is not a terribly filling food. However, you will frequently get apples if you use wood for anything, as they can drop from most non-pine trees. When building exclusively with wood, I often find myself generating a stack or two of apples without really thinking about it.
The other fruit you have available as a food is the melon. Melons are usually not found in the wild- only grown. Of course, that makes getting ahold of seeds especially difficult- melon seeds are most often found in the chests that you can locate in ‘dungeon’ rooms that hold monster spawners. They may also be found in the chests you can locate in strongholds, but it is far easier and more frequent to find a spawner room. When you harvest a melon, you will usually receive three to five melon slices. While these are even less filling than apples (both in terms of how long they keep your hunger bar full and in how much they restore- a single meat-stick), growing even a small plot of melon vines will keep you supplied with stacks and stacks of melon within a couple of hours of gameplay (or a few days, in game time).
As far as grains go, for all that you have wheat (and likely will find yourself growing a lot of it) and three different kinds of seed, the only foods you can make from wheat are sweets and bread. Loaves of bread still only fill two and a half meatsticks on your hunger bar, but they will keep you full a bit longer than apples, and notably longer than melon slices. They’re also harder to gather a lot of than melons or apples, since melon slices come in large quantities and you’ll likely find yourself with apples just as a matter of course when you gather wood.
The cookie is a very strange food these days. First of all, despite that it requires both wheat and the rare cocoa beans to craft cookies, cookies are the least filling food there is, each one only filling half of a meatstick on your food bar. Second of all, cookies are crafted in stacks of eight, and eight is the maximum stack size for cookies. This makes them, despite the difficulty of getting them, the single worst food in the game, particularly given that they don’t keep you full very long at all.
Cake is by far the most unusual of the foods- requiring not only wheat and an egg, but also buckets of milk and multiple units of sugar to make, the cake is not a food that is held and eaten- instead, a crafted cake must be placed, and then right clicked like a placeable tool. Once a cake has been placed, it can be right-clicked six times- each time, you will eat a sixth of the cake and refill one meatstick on your hunger bar. Cake does not affect how quickly you get hungry again, however. Even more interesting, the cake can be used as a half-block- because it is one. In this way, cake behaves like a slab, except that you cannot place cake on a slab to make a full block- instead the cake will ‘float’ to the space above that block. This makes cake, while not terribly efficient, rather fun to have and use.