What tasks or activities put you in a "flow state"?

Any task puts me into flow state if I can do it long enough uninterrupted. It happens quickest during soldering. The fumes might play a role here. 

Soldering.

When I was in my twenties and thirties my flow state clicked in after 11pm. Nowadays it's more event driven than time driven. E.g. give me hardware to tinker with, especially with soldering, and that's me zoned in / zoned out. Then LOL. The big distraction must be the Element14 website. Distracting me right now. As I often say to the wife... I'm a legacy single processor model... not very good at multi-tasking. It's 100% at something or NULL result.

My days can be defined as turbulent flow most of the time.  Watching a good sci-fi movie can be more immersive.

It is ironic D you ask this question.

I don't call it flow state but something more sinister. TF-Target fixation. OO-Objective Obsession. PB-Praxis Brain.

It has been noted that fighter pilots can fly their aircraft right into the ground if they become to focus on the target. I face this with problem solving. 

The Red Pitaya Roadtest is my example. I would like to have more success on this RoadTest than I have had but that expectation might be unrealistic.

Too much multi-tasking during the day to get into a flow, but if I’m left alone in the evenings I’ll lose track of time debugging hardware or software.

reading a good book suspends time for me.

I always thought of it in terms of me having a "one-track-mind" which means I'm very often in a flow state. For example I don't turn on the radio when driving a car because that can switch my attention from driving. I can't focus on both driving and the radio. I can ignore the radio, which means there is no point to having it on.

At work there are a lot of interruptions which limit the duration of flow states and meetings are a hopeless tangle of disjointed threads yanking in all directions, but whenever I am alone I slip into a flow state, whether it is designing, building, troubleshooting, reading or just daydreaming. In sports it is called being "in the zone" and it makes an enormous difference to performance.

I find that a complex problem gets me in the "flow state", but a more mundane task doesn't. In fact, if I'm working on something tricky I need music off, but with more mundane task I actually prefer music on and will often chose to context switch between multiple smaller tasks.

Some times when I am writing the frimware, I think about 1 to half hour daily, that I have a lot of time so I can leave it for now, it had improved my productivity a lot.