The other option was waking bigby up and being responsible for tthe aftermath of his wrath. He took the loss for his friend.

I'm sure in the book there's an inner monologue section of Spud's where he reasons that he's still upset about Begbie knifing the American in Edinburgh, as well as glassing the guy down in London, and so he doesn't mind Begbie getting ripped off. Spud is a very peaceful, non-violent guy. Plus I'd imagine Renton gives him a spare key to the locker thing before he leaves, so Spud knows he's getting some money.

Too high on dope to stop him

>>218232073
He had no idea he would leave him anything. He just knew there would be a violent outcome for Renton.
>>218232080
He was fully wake and understanding of the situation. He didnt want to risk waking bigby up.

that bag got jipped and no cunt leaves here til I find out what cunt did it