Workout bag packed and ready (the night before or always-ready) removes friction. Decision not to train can't easily be 'I haven't packed' if bag is ready by door.
What to keep in it
Workout clothes. Shoes. Water bottle. Towel. Pre-workout snack. Hair ties. Phone holder. Anything else specific to your training.
Pre-pack means the only decision is to go or not. Many people skip when packing is barrier. Removing it improves consistency measurably.