Lonely planet is good but try to pack too much into the book, therefore lots details are missing. Fordor's is better for hotel and food, Eyewitness is very good for city sightseeing.
GPS:
don't understand why most ppl dont bring one, even you dont have a map load into it, you could still marking the coordinates
water filter:
there are water bottles that come with filters, only few oz, use as water bottle if you dont need the filter, but it will come handy from time to time