There is large variety of daysacks, but current trend is packable lightweight daysacks. They are so great. Usually weight only 200-300g (7-9 oz) and are very compact.
I am in no doubt that in most cases you don’t need backpack then you are “backpacking”. What is definition of backpacking according wikipedia – “use of public transport as a means of travel, preference of youth hostels to traditional hotels, length of the trip vs. conventional vacations, use of a backpack, an interest in…