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