Well, it is common for snakes to lose interest in food while in shed. If your snake refuses to eat, you should wait another week before offering food.. continually offering several days in a row can actually stress them out.

Now, I don't mean this to be mean, but it's quite inhumane to keep a rat for a day or more without proper food and water. I would highly suggest having a small cage with a water bottle and some food ready just in case this happens again. Letting a domestic animal loose in the wild is never a good idea either.. for many reasons.

For rat food you can use dog food in a pinch..

Since your snake is 3' or so.. I'd say it's perfectly safe to feed him every other week. Since this is the first time he's refused food on you (at least that's what I gathered from your post) you may not need to do that, but wait a week before offering food again.