Here is the full list of all 27 Zombieland: Double Tap - there are Road Trip achievements worth 1,000 gamerscore.
Last 88 minutes in a single Horde Mode
Fully upgrade Special Meter
Fully upgrade Health
Earn ZKOTW 12 times
Beat a level with 4 players, each playing a main character.
Beat all the side missions
Fully upgrade Speed
Gain a kill with every environmental hazard
Beat the tenth level
Travel from L.A. to D.C. in under 5 hours and 45 minutes
Kill one of every zombie
Fully upgrade Weapon Durability
Beat the ninth level
Collect 100 Twinkies to celebrate 100 years of Hostess!
Beat the eighth level
Beat the seventh level
Fully upgrade Weapon Damage
Beat the sixth level
Beat the fifth level
Beat the fourth level
Earn a kill with every weapon
Beat the third level
Beat the second level
Beat the first level
Kill six zombies and light yourself on fire with a single Molotov
Kill three zombies with one sniper rifle shot
Kill four zombies with one shotgun blast