The "etc" can include trekking poles, stove sometimes (sometimes not, hard to tell what will get them going), some foods might come under the liquids or gels thing (for example, some people like to bring olive oil to put in their food).

The tricky thing is that not only do rules change, but enforcement can vary. I have a friend who swears he always brings his trekking poles as carry-on with never a problem. Except the one trip where he and I flew together and he was stopped at the security area after I had gotten through, had to go back and check his poles separately. Then the poles for some reason came out in the "oversized" luggage place on the other end (which I guess was really "unusually sized" luggage output), so we wasted more time on arrival trying to find his poles. PITA.

IMO, better to just plan on checking luggage if you're flying unless you really can get by with no poles and no knife on your trip. Hiking the Camino de Santiago in Spain I did just that, though I did buy a cheap knife on arrival and gave it away at the end.

When my wife and I fly to hike somewhere, we typically check one bag between us, and use the other backpack as a sort of shared carry-on, and that works well. I think it would be nice if airports with a lot of backpacking options in the area had a little business where they would rent poles and knives, sell stove fuel, and hold your protective duffel bag for you. Probably not enough demand, but would be nice! Alternatively, a hostel in the area could do at least some of this perhaps.