What does add the most fiber to my diet?

Plants. Adding more plants (fruits and veggies) will add fiber while helping add a substantial amount of other nutrients that are also healthy. There are lots of palatable ways to do this, even if you don't like fruits and veggies. Do internet search for recipes you like, then look for ways to add fruits & veggies to them. If you are trying to treat a particular condition, ask again w/more detail. Thx.