When Pete and Adam return from the mini-mart with no alcohol Pete says "and you've already paid for it." But Adam had dropped the box of bottles on the floor (smashing them) before he had got as far as the cash till. In light of the following incident it seems unlikely that the shop owner would have made him pay for them.
Adam repeatedly states his birthday as being April 18th but, during his birthday party when he visits the local minimart to buy more alcohol, the CCTV in the shop shows the current date as 13th June.