You unlock memory levels as you obtain Gold medals throughout story mode. Once you have 25 Gold medals all the unlockable memories will be ready to play. There are 2 "memories" that will show up at the end of the list once you have completed the game, regardless of your medal count.
Many of this levels take less than a minute; you are given plenty of time (sometimes 9 minutes) as there is usually some activity that you can do just for fun, whether it be play soccer, cause extra damage, run an obstacle course, but the way to complete the memory is to focus on the objects appear when you hold
and get them on the truck.
The amount of objects varies from 1 object to 56. The 56 item memory has conveyor belts all over the map and is quite fun as they all end up in a shredder. Once all the memories are completed and have a check mark beside them the achievement will pop.
Some examples of the memories are:
- carrying a box through an obstacle filled canyon while a boulder tries to crush you
- carrying a couch through a traffic jam while the cars move to either open the way or block you
- digging through a mountain of boxes to find the cash box at the bottom
- hopping from house to car to boxes to deliver objects during a flood
- navigating a maze of rakes to load your truck
It was fun and once I had all the memories unlocked took me 15-20 minutes total to complete them all.