How can I remind myself to lock a rental bicycle at the end of the ride?
Counting Method

Count the number of steps you must perform at the end of the ride and then refuse to leave the bicycle until you have done all the steps.
For example - End Of Ride Steps:


Park the bike
Lock the bike
Get the backpack


That's three steps.
When you are ready to leave the parked bike you have three things you must do. Don't leave the bike until you have done the three things.

Acronym Method

Create an acronym of the different things you need to do at the end of the ride and refuse to leave the bike until each letter is identified.