Originally Posted by oneclick

First question: whether to add spacers or cold-set depends on how much load will be on the bike and how good you are at cold-setting, and by how much bother you'll find it to have to spring it back together anytime you take the wheel out. Forks are tricky because you have to get/keep two independent surfaces correct in 3d relative to each other and the centre-line of the steerer tube. The farther the dropouts are from the cones the more stress on the axle, if the rider is light this is less of a worry, and 3-4mm on each end is probably not much - plus you can likely reduce it by employing the proper solution to your second question.

Second question: yes there are washers etcetera, a good hub's locknuts will have a surface that bites into the inside face of the dropouts, and QR nuts usually have the same for the outside surfaces. Plain axle nuts are often supplied with toothed washers, either captive or free, for the same purpose. However, the best thing to do is this: Tighten those nuts like you mean it. It's what was done before the CPSC regulations came out.