Contrary to its name, the Satchel cannot be made from a rune bar, nor does it provide any bonuses. The "Rune" may instead refer to its shade of colour, rather than the material it's made of.
Multiple satchels of the same type do not stack in the bank.
Satchels were once tradeable among players. However, with the introduction of the Grand Exchange, they became untradeable. When satchels were tradeable, they were commonly used to trade Triangle sandwiches which were untradeable.
Satchels could be used to smuggle food into Castle Wars for a short period of time before the glitch was fixed.