wild foods

We are travelling from UK to BC & WA for 6 weeks in late August. 3 weeks will be spent in B class RV. I am looking for tips on what wild foods we may be able to forage (and if it is allowed, for example picking wild berries) at that time of year. Also I would like to get a good, but small, book which will help with identification, as I know that there are some very different plants in America. Any help would be much appreciated.