I love my bike! It's based on an old racing cycle frame combined with a lot of nice and rare bicycle parts. I do not want it stolen, so I carry it every day, 100 steps down, 100 steps up. Sometimes living on the 4th floor is a real disadvantage.
Adding a carrying handle seems useful and in fact it is working very well!

 

A while ago, I saw a guy clamping an old plastic bottle between the seat stays of his bike, to use it as a fender. It doesn't look very stable but it was a great idea anyway!

This 3d printed mount works with most plastic bottles, like Coke, Evian ect. You can just clip it on your bike - no glue or screws needed!
I've used a bottle which I've cut before. Technical, there is no need to halve it but it looks better this way and it's done easily.

 

On a bike you're fast as lightning? ...
This is a pair of lightning caps which fit nice on Schrader valves!