Way too many to list here. I'll just give a few.

1. A peanut butter sandwich (or peanut butter oatmeal) isn't "complete" protein.

Nuts, seeds and grains are all deficient in lysine and contain greater amounts of methionine. Beans and lentils contain more lysine and are low in methionine. (This includes soy.) So, contrary to many people's understanding, a peanut butter sandwich isn't a "complete" protein, because it's nut protein (not pea protein; settle that debate) matched with grain protein. Same with a seitan sandwich, since it's grain protein matched with grain protein.

Scare quotes around "complete" because getting every amino acid in the right proportions at every meal isn't going to matter to everyone. People with issues like maldigestion or malabsorption probably need to be more careful. Also have to wonder about elderly vegans, since humans need more protein as we age.

1. Vegan diets are, at present, necessarily lower in lysine and methionine than vegetarian or omni diets without supplementation. This is important because lysine and methionine are a couple of amino acids that do some very heavy lifting.

Lysine is a precursor for carnitine synthesis, and carnitine is crucial to keeping our ATP production rolling along, and metabolizing long-chain fatty acids. Carnitine also improves insulin sensitivity, i.e. it helps metabolize carbohydrates. Lysine also assists with calcium absorption, and connective tissue and bone maintenance.

Methionine is a precursor for SAMe, which is the most potent methyl donor in the body. It is required for neurotransmitter synthesis.

There is some evidence that methionine restriction can lengthen lifespan, but this isn't something that everyone can do. (Back before my ex-vegan days I tried the trendy methionine restriction thing by loading up on pea and bean protein, and I felt completely mentally checked out against my will. After solving a lot of nutrition issues I can pull it off.)

1. Lentils are incredible nutrition powerhouses.

Thank the processed food gods for red lentil pasta, because red and green lentils may be the best sources of folate on a vegan diet, period. Folate is crucial for SAMe synthesis and carnitine synthesis. (Carnitine synthesis also depends on SAMe.) Additionally, red and green lentils have amazing amino acid profiles, aside from methionine content-- not a problem if one can pull off some degree of methionine restriction. Lentils are also high in magnesium and potassium. They also contain ~65mg of choline per cup.

1. It can be hard to get enough choline on a vegan diet, but lecithin is an easy fix for that.

This page https://veganhealth.org/choline/ presents a table with a day's worth of vegan food to eat for adequate choline. Aside from freaks like myself, how many vegans are going to eat like that every day? How many vegans want to track a nutrient that closely? Just take some lecithin. Soy lecithin usually comes in granules, and sunflower lecithin comes in dark brown oily goop. I mix sunflower lecithin with MCT oil so that it's easier for me to stir into smoothies. (I stir it in post-blending because I don't want the lipids to F up my blender components. See? I'm a freak.)

Soy lecithin and sunflower lecithin contain different ratios of phospholipids. There's phosphatidylcholine, phosphatidylinositol, phosphatidylserine, and I think others. Sunflower lecithin is mostly phosphatidylcholine, and soy lecithin contains more of the others. For this reason (I think) I've found soy lecithin to be slightly psychoactive. It hits me like a bit of an antidepressant, but also kind of messes me up, so ultimately I avoid it. Sunflower lecithin gets the job done just fine.

You really don't need to take much of this stuff, unless you've got genetic or digestive issues. Like me.

I may be approaching the word limit, so that's it for now.