Here is the full list of all 25 Totally Reliable Delivery Service achievements.
Unlock the mule.
Remain airborne for 10 seconds.
Complete first delivery.
Change your clothes.
Complete 10 different deliveries.
Complete 50 different deliveries.
Complete 100 different deliveries.
Find the tiny island.
Visit Gasa Research Facility.
Visit Keister Island.
Visit Happy Clam Resort.
Unlock the buggy.
Unlock the pickup truck.
Unlock the helicopter.
Unlock the rocket booster.
Pass gas in a biplane.
Put treasure chest on sloop.
Bring the luchador mask to wrestling ring.
Bring the conch shell to top of mountain.
Return the satellite to GASA.
Bring banana to room 5 at Banana Motel.
Bring grill to Dad Statue in Golden Ruins.
Bring foam hand to Booster Club Arena.
Lose pants in tornado at Happy Clam Resort.
Find the big secret bear.