There are a lot of great vegetarian recipes out there. You should probably ask ahead of time what your friend does not eat. Usually vegetarians make a dish and bring it with them, but if you would like to provide for them, plan ahead or maybe ask them for a recipe you can try. This food is crazy. In many places you can get vegetarian items that you never could before.
Most stores sell soy milk or rice milk that can hold their own next to cow milk.
There are even oat milks and almond milks for baking. Asian markets also often sell fresh tofu and veggie products. Morning star has a great line of veggie burgers and bacon. Smart Dogs even has veggie hot dogs. There is even veggie and vegan cheese.