There's so many cool things one can collect.

I once collected tons of pretty rocks on a trip and forgot them in my carry on luggage and got stopped by security at the airport and got really sad because they weren't gonna let me keep them.

(age 11)

Anyhow... Instead of collecting cool rocks, you can collect stuff like this! Definitely more probable to be allowed aboard a plane.

It's certainly lighter. Less efficient as a melee weapon though.

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(and I get paid. I don't get paid if you pick rocks)