Rimmer's rum is in the bandit camp, you just have to look high and low for it (mostly high).
Half way through the camp there is a gate, with a platform and a ladder you can climb up to get on top, where there are a couple people (one of whom has a quest for you). Across the top of the gate there is a ledge where you can find the rum.
Pause the game and you will be able to bring up the Item and Skill List from the Pause Bar, to use items (potions, etc) or any skill that does not need a target (or at least with the Xbox version when you paused and hit a shoulder button to bring up the item/skill menu, you could only use skills that didn't need a target).
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