I have a problem. Not so much a problem, more a lack of proper power tools. As such, when I am making cutting boards, tables, benches, etc. I have to use my hand planes to make wood flat. Of course, I try to buy the flattest stock I can, however, as wood sits around the shop, it will sometimes warp a bit. Take this beautiful rough sawn cherry I picked up a few months ago. While most of it has been flat and very easy to work with, some of it has warped over time.
I know it’s hard to see in this shot, but just below my trusty #5 is a bunch of pencil marks. These indicate the high spot on this side of the board. To flatten, I use my #5, #4, and on really rough stuff, my #8 planes to flatten things out. I remove a little material at a time, checking often that things are nice and flat. Once flat and sanded smooth, each piece is hand rubbed with either mineral oil or wax.