Yes, you should carry a 25 litre frame-less day pack. This should contain a rainproof outer layer (usually just a raincoat is sufficient), an extra warm layer, shade hat and/or warm woolly hat, water bottles or water bladder (e.g. Camelbak), hiking poles if preferred, camera, mobile phone and passport or other personal items. If you are doing full day more strenuous hikes it may also be necessary to carry some of the picnic food or gear.
