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 Weapon Durability
Earn ZKOTW 12 times
Fully upgrade Speed
Beat a level with 4 players, each playing a main character.
Gain a kill with every environmental hazard
Beat all the side missions
Fully upgrade Health
Travel from L.A. to D.C. in under 5 hours and 45 minutes
Beat the tenth level
Kill one of every zombie
Beat the ninth level
Beat the eighth level
Collect 100 Twinkies to celebrate 100 years of Hostess!
Fully upgrade Weapon Damage
Beat the seventh level
Beat the sixth level
Kill six zombies and light yourself on fire with a single Molotov
Earn a kill with every weapon
Beat the fifth level
Beat the fourth level
Beat the third level
Beat the second level
Beat the first level
Kill four zombies with one shotgun blast
Kill three zombies with one sniper rifle shot