Ill see if I can find one of those at Freedom. And are slings really necessary, or can I get by without them?
You don't need them. They're nice to have though.
Similarly, you don't need a plate carrier/chest rig. lol.
There are a few things that really change the way you play and how comfortable and effective you are:
Proper clothing (decent boots, ripstop stuff that's tough enough to keep out most thorns and bugs and whatnot)
Plate carrier/chest rig with pouches to hold your gear.
Dump Pouch
Sling to hold your primary when you need your hands free(climbing, radio use, etc) or switch to a secondary(failure, rules on gun hits, etc...).
Camelbak or other hydration carrying system (keeps you hydrated, moving, and comfortable)
Experience (makes everything better and lets you know how to use it. lol)
Once again, you don't NEED one. They're nice to have.