Urethane O-Ring, most commonly used on the end of tanks, as well as some bolts and various other locations throughout the paintball industry. Save money and buy a 10 pack!
Safer than a barrel plug, this will attach to pretty much any paintball marker and comes in camo.
This is the standard in safety protection for your neck. Comes in black/grey colour scheme, and keeps you from getting any nasty marks on the neck that you don't want to explain tomorrow.
Marker oil is needed to lubricate the o-rings on the majority of entry level markers, and can be used in all sorts of regulators.