Saddle up
Definition 1 of 2
Pro Tip 1/3Literal Use
Directly refers to the action of putting a saddle on a horse before riding it. 
The rancher told me to saddle up before sunrise.
Pro Tip 2/3Western Context
Often used in Westerns or talking about cowboys to show it's time to ride horses. 
In the movie, the hero would saddle up before chasing the bandits.
Pro Tip 3/3Preparation Hint
Implies preparing for an activity, not just putting on the saddle. 
Make sure to saddle up your horse with extra supplies for the long journey.