Europe is a big place, and legal restrictions will vary from country to country. Can you be more specific about your countries of destination and the type of backpacking you intend to do? If you're going on outdoors-y kinds of hiking trips , a large folder or a fixed blade knife will probably be acceptable in most places. If you're just going to be bumming from one city to another, though, that won't be the case. In any case, I think you'll find that a SAK will be fine pretty much anywhere. I should add, too, that, especially if you plan on carrying a knife, you should be on your best behavior and try to present a good appearance. The police are much more likely to stop you if you're rowdy or if you are particularly radical looking or unkempt. Bear in mind that the police in Europe don't need reasonable cause to stop you and do a routine check; if they don't like your looks, you might get hassled.