It's nice that these two couples do things like going on walks rather than just go to pool parties. It shows that they really all do get along. In addition, a hike is a good way of getting Sammy out and about rather drinking himself into a stupor.
'Mantha doesn't just tell us that Sammy is good at finding places but practically orders everyone to let Sammy lead. Maybe it's because he will turn to drink even more if he doesn't get his own way. However, what they don't know is that Sammy was always looking for a pub. 'Mantha and Lynne probably think that George's comment about Sammy smelling drink is a joke when in fact it isn't. Sammy can smell drink from a mile off. To be honest it's not that difficult to find a pub when going for a ramble so it was bound to happen sooner or later that Sammy would get his drink on. It is a problem that they really need to deal with, but after the pub lunch.