Quick release bags and on-bike stuff?
 

My headlight attaches with a rubber band and has an external battery pack, plus carrying my phone and other small essentials.
I'm looking for a low riding, quick release handlebar bag that I can sling over my shoulder and toss my headlight into if I make a quick stop on the way to or from work.
How much stuff, such as a headlight or computer, do you remove from your bike when you walk away from it?
Experiences? Suggestions?

I would not leave anything of value like a light that can be easily removed on the bike unattended. I purchase front lights where the light attaches to a mount and leave the mount on the bike. Rear lights also come with mounting brackets. Generally, I don't leave my bike unattended except to run in to get an iced latte. I take the lights with me but leave the seat bag since I can see the bike from inside. But there are enough rotten people out there that it's best not to take chances.

We have an employee only badged bike room at work. I leave my seat bag but not my lights on the bike. And I have a hefty Ulock. People leave bikes there unlocked or with the cheapest cable locks that you could probably cut with a nail clipper. I don't believe there are any cameras in the room. My fear is that the lock stops working and the room is accessible from the public parking area.

If you leave your bike unattended often, shop around for easily removable bags. Check out online stores for ideas (Performancebike, Nashbar, Jenson, etc).

I have pretty expensive front and rear lights, an mp3 player, and a good speaker on my handlebars. I take them all off and put them in my quick-release Topeaker MTX DMX trunk bag/pannier on rare occasions I leave the bike alone.

I leave the blinkies but take my main headlight, bike computer (speedometer) and water bottle with me. At night I have another headlamp and blinkie but they are on my helmet, so they go with me anyway). I have been using a backpack for decades, racked on two bikes, worn on one rackless bike.

I have a permanently mounted dynamo light with a Pitlock bolt securing it to the fork crown. I always remove bags and computer when locking the bike outside. I have a bike locker at the office and can just leave my helmet and stuff with the bike there.

I looked for a quick release handlebar bag and couldn't find one. BUT, a regular backpack can be modified to do the trick, rolling up to mount and with an attached brace to hold off at the stem or head tube. I won't say that it's easy, but I'm sure that one could work out a variation of this. I've been using this most days for months and it works great. Rolling up means that it can be stuffed to various amounts, or used as a backpack if completely full. Or when off the bike.

I took those hooks off and inserted flat hooks into the bag's padded straps instead so that's an older photo. Putting it on I set the hooks on the handlebar, pull an elastic strap around the back of the stem and that's it. To remove it I simply pull straight up and it instantly transforms into a backpack!

The keys to this are: having some way to keep the bag rolled up, hooks secure over the top of the handlebar, a strap of some sort around the back side of the stem/head tube, and a built-in stand-off from the stem or head tube. If you have all of these, the bag is kept from sagging, onto the wheel for example on more aggressive road bike geometry.

The same as I remove from my car when I park it. Nothing. No computer, and the lights are built in. As with the car.

I use Ortlieb's 6s Plus. Really nice and compact handlebar bag. Good QR system.

I was looking for a small keys, wallet, dumb phone bag, but the cheapest ones were $15 and didn't want to fit my bike, so I found a nice camera case at a local thrift store for $2.50 and attached it with a couple of dollar store cat collars. If I was more ambitious I'd sew a piece of double-sided velcro to each D-ring; Real Soon Now.