When completing laps of the Ape Atoll agility course you can earn a monkey backpack! These are obtained automatically whenever you reach the lap count required for each backpack.
Monkey
Required laps
Karamjan
100
Zombie
250
Maniacal
500
Skeleton
1,000
Kruk jr.
1,500
Princely
2,000
To view your total lap counts on all agility courses, you can use the +m lapcounts command.