Tying crap down is both art and science, although some folks manage to avoid both approaches. We call them yard sale people, 'cause that's what it looks like when their bombproof rigging job blows apart and scatters gear hither, thither and yon.
Do not be a yard sale person. Use reliable straps like these 3/4" nylon ones from OR. They have tension buckles, which I prefer as more reliable than quick-release styles for critical applications like tying down a load on a sled for glacier travel.