I scrub plane and bevel the edges. This smooths out the wood, and makes sanding easier. Also, by trimming the sharp edges it gives the box a nice worn look.
For the gaps in the wood (there are a few, because the wood is irregular) I'm filling with putty. This problem could also be avoided if I squared up the edges with a table saw first. Maybe I'll try that next time. However the spaces in between the boards adds character. I only fill them so you can't see daylight in between. Once I get everything sanded down it will really look proper.