Agree with FitGirly - in the long run, a storage unit might run a few hundred $ but when you're looking at getting so much more for your house, it seems inconsequential to spend it to potentially speed a sale. Declutter anything and everything that you can!
An old trick, but a good one, bake something early in the morning that has cinnamon in it - or fresh bread - that smells like HOME to folks ... and then donate it to a VFW or a nursing home or to your humane society workers or something - muffins, etc., are welcomed most places like that.
Fresh flowering plants near the entry are nice if you can. Also what I have is a TOP 10 reasons I love my home listing that I keep updating ... for when we want to sell. A friend and I did this to sell her home a few years ago after it wasn't getting any bites - whammo

not that it did it but it helps people see things they might not see in a few run throughs. Like I am on the end of the street and have unencumbered views of the sunset all year long...the more-than-ample closet space (take things out and store so they don't look packed to the rafters!) ... basically highlight anything you think someone might miss that kind of "makes" your home to you.
GOOD LUCK!