There are several achievements available in Halo: Reach, and many of them are hidden throughout the campaign, waiting for you to explore the environment and find them. While some are obvious, others take a bit more snooping around to weed out.
To receive the No Picnic achievement in the game, you need to hop on over to the Exodus mission, which should be the seventh option in the lineup.
You won’t need to do too much leg work to grab this achievement. Watch the cutscene at the start, or skip it, and load into the game. You start the mission with a small amount of your health missing and a pistol. The beginning of the mission looks like a slaughter. Bodies are everywhere, with clear signs of a battle.
Make your way through the courtyard of the area until you see a door that’s opening and closing, never fully closing. Before you reach this door, you look down near a bench, and you should see a stuffed bear backpack on the ground, pictured below.
Stand in front of the bear, look at it, and then walk around the immediate area where all of the surrounding bodies. You might need to make a few circles of the area before the achievement unlocks.