When Mitch and Colin arrive at the hot spring near the end, they walk over a small arched bridge, past some women who smile at them. Mitch is wearing sandals, and Colin is barefoot. But when they get to the water and drop their robes, Colin kicks off a pair of flip-flops that suddenly appeared on his feet.
When Leslie's cousin and her friend arrive from Nuuk, Greenland, the men pick them up at Keflavik airport, but flights from Nuuk arrive in Reykjavik, not Keflavik.
After the men arrive in Iceland they're shown supposedly driving to Reykjavik from Keflavik, but as the ocean is shown in the left of frame, they're clearly driving away from Reykjavik, not towards it.
Mitch tells Colin he has purchased first class tickets to Iceland. They are subsequently shown arriving in Reykjavik on Icelandair. Icelandair offers business class, but not first class.