My tip is an "activity bag". I always keep a zippered tote bag stocked with various books, travel games, small toys, stickers, magic markers, paper, etc. right in my trunk. That way if we're out somewhere and decide to go out to eat we've always got something to keep the kids occupied while we order our food, wait for it, linger over coffee (ok, we don't actually make it quite that long very often, but a girl can dream can't she?), etc. It's also available if we need it for medium-sized trips if the kids' music has lost its appeal or if we find ourselves in unexpected traffic (I'm not a martyr, for long trips we break out the dvd player). I rotate the contents of the bag periodically so that it includes both current favorites and things they've managed to forget about long enough for them to become interesting again.