Lefty friendly, i would assume your interests would align with trying to help the common person, and climate change adaptation.
Your stated experience, and interests sound varied, and present you as a highly active person.
Combining these things in my mind i instantly thought you should get into food system adaptation for a warmer more volatile world. Where people could really suffer horrendously with climate change is if food production systems break down. We need smart people, willing to try new approaches in that system. Farming where i’m from is bed of roses, and a lot of the skills you listed farmers here would likely use, so its probably the same/similar elsewhere.
So specifically i’s thinking organic farming, or permaculture, or perhaps a more scientific route such as propagation of new tougher varietals.
Logistical needs are also important, the amount of energy used to transport food must be immense and so that could be an avenue you could go down marrying your comments about mechanical engineering to the idea of improving the worlds food production systems.
Good luck with your ongoing career, whatever you decide.
Tickets/Voucher for a rock climbing centre could be up his alley.
If you want something that will last you could get him a powder bag, or his first Carabiner as well.
Be prepared that the climbing place might not let him use the Carabiner in conjunction with their equipment though, so it might sit around until he got his own harness if he ever went that far. Powder bag would be all good.