It is difficult to eat enough fiber. My trick is that I keep a sealed plastic container in the refrigerator with a mixture of cooked spiced beans. I usually just use black beans and garbonzo beans. I vary the spices, but usually use some combination hot spices. It is easy to then add these to whole wheat pita sandwiches, soups, salads, etc. This way I get a lot of fiber and extra protein.
Just eat lots of veggies and leave the skins on for most fruits and veggies. If you're really struggling for some reason, lentils are a really easy food to eat that's packed with awesome nutrients.
and makes the distinction between soluble and insoluble fiber. Quick source: 100g of almonds has 12.5g d.f., as well as a wealth of important vitamins.
Sweet potato is a cheap and easy dietary fiber source. Also good slow burning source of energy. The betacarotene on it, in my opinion it is unclear it is good or bad for you. I think betacaroten daily maybe not good, maybe some varieties of sweet potato has less betacarotene
Anyway is a good and cheap food, can keep you alive on frozen winter.