Here's a traveling wave tube amp that does 5 kilowatts: https://www.arworld.us/post/5700TP12G18.pdf?44385.7040046296

The tube on the cover of this book is 1 MW at 90 GHz.

https://www.amazon.com/Tube-Guys-Norman-H-Pond/dp/0981692303

It's for an airborne ADS (i.e. pain ray). Good book if you want the detailed history of microwave tubes.

Walkie-talkies are mostly .5 to 5 watts, but you can get ones with 20 to 40 watts. I'm not sure how legal those are.

If you're in the US and have an Amateur license, you can generally transmit with up to 1500 watts PEP (Peak Envelope Power). Some lower limits apply; for example a Technician licensee is limited to 200 watts in the HF bands, but may use the full 1500 watts in most VHF/UHF bands.

There is no legal distinction between a handheld and any other kind of transmitter. A transmitter is a transmitter.

There is a legal requirement to use the minimum power needed to carry out the desired communications, so you should not blast out 1500 watts at all times. Especially not next to your head!

http://www.arrl.org/frequency-allocations

Whether or not they're legal, they're a bad idea to use next to your head.

Higher power handheld transceivers usually feature a corded microphone to allow increased distance between your head and the antenna.