I really like things that multitask. Which is why I have been enamored for some time with the "A Day in the Park Backpack Tote" pattern from Liesl and Co. It can be carried as a tote or a backpack, thanks to a clever design in the straps.
I would love to have a bag that I can wear as a backpack while biking to work, but that also functions as shoulder bag when I am on foot. And I have never been down with slinging messenger bags across my back while biking. I know it works for a lot of people, but I have a personal vendetta against messenger-style bags.
Unfortunately, the pattern for the "A Day in the Park Backpack Tote" pattern is currently unavailable, not to mention there are a few things missing that would make it an appropriate bag for me (e.g. too shallow for carrying a computer and my lunch to work, and no top closure = not good in the rain).
Therefore, being the engineer that I am, I have begun to design a bag that will meet my needs, which will be called the "Biking to Work in the City" Backpack tote.
It will look more like a vintage bowling bag, and have a similar convertible strap mechanism. I will be able to alter a pattern I created long ago for my favorite bag to carry when I am just "Walking to Work in the City."
It is one of the earlier bag patterns I ever drafted, and was inspired by Amy Butler's Sophia Bag., as a learning experience on sewing a bag with piping and a zipper closure.
I have also been working on a men's version for my husband who also bikes to work in the city.
The design for his bag has been a larger challenge, due to a different system for converting it from messenger-style to backpack-style which requires changing the orientation of the bag while making sure the contents of the bag remain secure. I might be crazy with this one, but my husband gets his wishes granted because they are so few.
p.s. yes, all my sketches happen on gridded engineering paper. it's my favorite writing surface.