I happened to grab two sources I bought a pack of 100 golf pencils at a golf store sale for $1 per pack so I bought two.
I also stash a bag of pens from giveaways, college swag, and hotels in my car in the glove compartment.
Lastly I have a keyring that has a pen attached to it so I hope to not forget a pen with me or I have bigger issues if I locked up my car.