There is nothing worse than getting into your car as you prepare to leave for work and discovering your battery is dead. You could call AAA - if you have a membership, your parents - if they live close by, or a friend - if you have any of those. Regardless of whom you call, by the time they get there, you are going to be late to work.
The other option is to buy a portable battery pack that doubles as a car jump-starter and keep it in your trunk for just such occasions. There are a ton of different companies that make these things, and today, one of them is on sale.
Nekteck's 12000mAh battery, with 600A peak output, can be yours for $49.99 after a $30 off coupon code on Amazon. It'll jump start a 5L gas engine, or 3L diesel engine, up to 12 times on a single charge (good for an after-game tailgate party where everyone passes out and forgets to turn off their headlights).
It also has two USB ports that you can use to charge your other electronics and an LED flashlight which is useful for seeing stuff in the dark, like your dead car battery. Bundled with the battery is a 12V car charger, a MicroUSB cable, and jumper cables that plug into the power bank. Oh, and it also has a zippered case to carry all this stuff so it won't clutter your trunk.
Reviews are solid, with a 4.9 star rating. Sure, some of the five-star reviews are from people who got the device for free in exchange for an 'unbiased review', but the bulk of the positive reviews are from legit customers. The battery has a 12 month warranty and is backed by Amazon's 30 day return policy, so if it doesn't perform as you expect you are covered.
Use coupon code NG9NY4DV at checkout to get the discounted price.