You should utilize all of the space in your storage unit. However, this does not mean to fill it to the brim with unnecessary items or ones that do not belong in storage units. This could potentially become very dangerous. Flammable items should not be out of your sight for too long. Therefore, keeping them in a storage unit would not be ideal. They would pose a risk to the rest of your items in the unit as well as the unit in general. This would most likely cost much more than the items lost, considering the potential damage that could be done to the unit. Food should never be stored away in a unit. This will cause rodents and insects to appear.
Plus, why keep something of immediate use in a storage unit anyway? If you are planning on using it as a post-apocalypse hiding spot, re-think that idea, find a better hiding spot, and store your non-perishable food there. Although it is rare you will use important legal documents, keeping them in storage further increases the risk of them getting stolen. Instead, keep them in a safe or strategically buried in miscellaneous items in your home. Make sure you do not use your storage unit as a place to keep your pets when you are not home. Not only is this a scarring experience for animals due to its lack of light and space, but it is also illegal.
Most people who love animals enough to get a pet would not even think of doing this, but for those that have thought about it, know that you can face legal consequences. Bicycles should be there for you when you want to spontaneously exercise but do not have enough motivation to go running. That being said, do not keep your bike in a storage unit because by the time you get to the storage unit to pick it up, you might lose the small amount of motivation you managed to pull together.