Best Natural Level-Up Moves:
Yawn. Totally throw stuff off guard, and basically allows a free attack if fused with a certain attack.
Body Slam. A viable option for a Level-Up Attack if you don't like Return. Also because the 30% Paralysis chance is hawt.
Crunch. Technically, Snorlax learns that. It helps for crushing Ghosts.
Best TMs and HMs (or just TMs actually :p):
TM01 - Focus Punch. Mainly to be used in conjunction with Substitute, but it causes destruction if used properly.
TM26 - Earthquake. If Focus Punch fails in duty, then Earthquake is beneficial. Also not to mention it crushes Electrics and other solid things with ease.
TM27 - Return. One of the best Normal Type STAB Attacks for Munchlax, next to Body Slam. Gets a maximum of 102 base power.
TM44 - Rest. Learns this through TM, or by level after evolving into Snorlax. To be used in conjunction with Sleep Talk.
TM82 - Sleep Talk. To be used in conjunction with Rest. Attacks while sleeping, which helps for absorbing status attacks.
TM90 - Substitute. To be used in conjunction with Yawn and Focus Punch. When the opponent tries to switch after Yawn, use Substitute to score a freeFocus