You can find daypacks with 3k to 3.5k cubic inches of inner space, which also serve as convenient carry-on luggage. A daypack this large is coming close to full backpack site.  When you look at the average or standard size daypack, you'll find that most offer from 1k to -cubic inches of space to stash your gear. You can't go wrong when selecting a daypack from any of the big name manufacturers like:

• Camelbak
  
• The North Face
  
• Coleman
  
• Jansport
  
• Kelty 
  

A very good day pack that will last for years should cost no more than about a hundred bucks ($100.00.)


Speciality Daypacks
You can also find daypacks that double up as baby or child carriers.  These make it easy to lug the little one around and provide a small amount of storage for diapers, wipes or snacks.  Another specialty daypack is the hydration pack.  These include a bladder that holds one to three gallons of liquid to keep your thirst quenched and your body hydrated during your hike.