I'd add a powerful handheld light for alerting other boats. ( and a good reason to buy a 250 lumen flashlight
The intensity of the light is usually not the issue. Even a quite modest light is readily visible for a great distance at night. As noted up thread, the real problem is that kayaks sit so low in the water, and are hard to see even in daylight. With even a modest bit of wave action, the kayaker will frequently disappear in the trough between waves.
Isn't the strobe for alerting other boats? As mentioned previously regarding the headlamp, a flashlight only shines in one direction rather than 360 degrees. A headlamp & flashlight should be included, but not for alerting/signaling. IMO, YMMV
In most cases, a kayaker will see other approaching vessels long before they can see the kayak. Almost any boat will have their lights mounted higher than a kayak. It is often best to paddle without a light on, preserving your night vision, and giving yourself a better chance of seeing the running lights of other boats a long way off.
In my experience, by far the biggest danger to kayakers is from high speed powerboats. If you see or hear one approaching, you turn on your headlamp or flashlight, and sweep it across them a few times. Then perhaps hold a paddle up in the air, and shine your light on the paddle blade (I sometimes put a short bit of reflective tap on my blades). A trick sailboats sometimes use is to shine a light up onto their sails, which becomes a very big, obvious marker.
Big ships will have their lights mounted very high off the water, and you should be able to see them far off. Big ships are also generally constrained to channels, and can't readily turn to avoid a kayak even if they see it, without risking running aground and endangering themselves. Likewise, due to their momentum, big ships can't readily stop. A large tanker may take miles to turn or stop. And big ships have to maintain some minimal speed to maintain control ("steerage way").
Hence the onus is on the kayaker to stay the hell out of the way of large vessels (the informal but very real "rule of superior tonnage"). Kayakers should be aware of shipping channels in the area, and avoid them. If you must cross a channel, look both ways then get across as fast as possible. (Much like a pedestrian crosses a busy road without a "walk light".)