I get flax seeds in bulk form (about 1.5 quid per pound) from health foods store. I grind them up in a small/cheap coffee grinder. They can be eaten like that, or somehting like raice bran (sweet) and/or oats can be added. I also buy cinnamon in capsule form (200 capsule bottle of 500mg cinnamon is like 5 quid). I'll open the capsule and add cinnamon to cereal. I also add various berries, nuts etc. Sometimes I also use apple pectin.
Presently, I like smoothies more than cereal. I add flaxseeds or chia seeds to whatever fruit I've put in my nutribullit blender