The Sunburn Pack Add-on for Rust has 7 achievements.
Be in a team where every team member is riding a Boogie Board or Inner Tube (minimum 4 members)
Take a photo of another player
Splash another player with a Water Pistol while that player is irradiated
Soak another player above the damage threshold using a water gun.
Get a kill using a water gun.
Get a kill with a super soaker pumped at the lowest pressure.