walking
A gentle stroll around the coast path of Gili Meno is not to be missed, and it is probably the nicest walk anywhere on the three islands. If you do this in the morning, there is no real preferred starting point. It is a nice idea to walk in the late afternoon, starting in the northwest at about 4:30PM, taking it easy to walk all the way around the island in either direction, returning to your start point at about 5:45PM. Then get yourself set for sunset behind Gili Trawangan 6:15PM-6:45PM.
snorkelling
There are several good spots for snorkelling, and gear can hired at almost any cafe or hotel for about Rp 30,000. The beach in front of Good Heart Cafe on the north western shore is as good as any, and you have a reasonable chance of seeing turtles in shallow water here. Also on the west coast, try the area close to the disused, derelict jetty formerly the landing point for the equally derelict Bounty Resort. The former pontoon here was sunk and has become an important dive site with a healthy reef life. If you snorkel off the east coast, be careful of boat traffic.
Blue Marlin
Full dive shop operation, with the same range of PADI courses and fun dives as are offered on the other islands.