Packs. There are lots of them out there. Here's one over at Airsoft Atlanta - it's the Shenzhen Tactical Ambush Pack. Cost is $26.99.
Up top, there's a pocket with MOLLE on it. This offers easy access to the user for a variety of smaller items.
Here's a look inside that pocket.
Below that pocket there is some bungee cordage where you can stuff in a jacket or something else that you want quick access to. There's also another small zippered compartment on the front of the pack here - more storage.
Here's how you get into that section
On the front, there's 1 large buckle. I like this as it make access quick and easy - you're not fiddling with a ton of different straps, snaps, etc.
The straps are comfortable. They aren't something I'd want to wear all day long with 20 lbs. in the bag, but they are comfortable and adjustable. D-rings allow for you to connect some gear to them as well, and the included sternum strap gives you even more control when you are wearing it.
There's padding and channeling for both comfort and airflow. If you are airsofting in the summer or hotter months, this will help you to stay a bit cooler when hauling your gear around.
Just to give you a sense, here's a look at a ton of MOLLE webbing that is available to you on this pack. This thing'll take pouches galore!
Here's looking into the main compartment. As you can see, there's a pouch to hold your hydration bladder.
And yet MORE storage in the other larger front section pocket.
In the outer pocket there is a place for some smaller gear and this internal mesh pocket as well. TOLD YOU THERE WAS PLENTY OF STORAGE!!!
Now I realize that Condor is kind of the standard for backpacks in airsoft. BUT I'd highly encourage you to consider this one. It's got (as you saw) a lot of storage, the built seems pretty solid, and it's under $30. Here's the link - check it out: GET THIS PACK OVER AT AIRSOFT ATLANTA.
Thanks for reading and keep on firin',