Ok, sounds like your family is taking one of the larger tour buses into Negril that stops at multiple hotels. You won't have to walk into town if you're looking for room supplies. If you cross the road, turn right(heading towards town), and walk half a mile, you'll find the Sweetspot mini mart which has plenty of alcohol and snacks on hand. If you walk down further towards town, another half mile and cross the road back to the beach side, you'll find another mini mart (Uno's I think, before Merrills III resort). Finally, if you think that won't be good enough, just grab a red license cab (negotiate price before you hop in) and have them take you to Hi-Lo in town (the driver will hangout til you're done shopping if you ask him).