If you don't want to use the backpack addon, try out kmkSquadStuff2 in the pending section of the editor depot. It includes a *really* simple gear bag system using the action menu.
With the script, you can use ANY ammo crate to simulate your team gear or individual pack. While it looks kinda odd to have an ammo crate appear instead of a nice looking backpack, it does solve the issue of magic ammo and keeps your "secondary" slot free for an AT4 or radio.
That was my main reason for not using the backpack addon, as it forced you to go through like four or five clicks to get a rocket launcher...in reality you can carry an M16 at-the-ready, a low-vector pack on your back, and have a rocket top-slung for fast readying. Radiomen also routinely wear a pack on their chest and the radio/frame on their back, while still carrying an M16 at the ready or slung. A backpack should NOT take up OFP's secondary weapon slot.
Which is why I wrote my gearbag scripts the way I did. If you want to throw 30 rifles into the "gear bag", go for it! You bought the game, you are free to play it however you want. I usually use it in missions for satchel charges, smoke grenades, and a few extra magazines. But depending on the ammo crate you choose to use with it, you could load as much as you want into it.
The script also supports using one object for the appearance, and placing the ammo crate underground...if you are a stickler for how it looks (and don't like to see the crate).
Edit: The other reason I dislike the backpack addon is that it can't be used with the CoC Scuba gear.
I've got a few missions where the player's squad inserts by scuba. Once they reach the shore, the player drops the gear bag (using my scirpts) and then orders everyone to remove the LAR7 and gear up for the mission (radios, rocket launchers, 2xSlot machine guns,etc...). It adds a nice touch of realism to a mission, making the player switch modes from exotic insert gear to mission gear. And it provides a tense time, as the gear swap has to be done quickly, lest the team be spotted by patrols or rovers. Kinda fun.