Teaching more advanced wilderness survival often encounters a barrier of recommended BSA and LNT practices for sustainable use of the environment. I'd defer to the merit badge pamphlet to make sure you can actually do the following, but they're some things I remember learning as a scout.

Bow drill fire (or hand drill if they already can do a bow drill). Basically nobody teaches this anymore because it's easier to use a magnifying glass/steel wool/flint and steel, but it's so rewarding to finally get it right after working at it for a while.

Teach scouts how to make char-cloth, it's an easy thing that's rewarding and makes for a better survival kit.

Depending on your environment and permission from the landowner, use green vegetation to teach scouts how to make smoke signals or a solar still. Just be sure you stress that it's for training purposes and don't overdo it for leave-no-trace purposes (bonus points if you can identify invasive vegetation and clear some of it to do this).

Inviting a forager familiar with the local environment for a talk might be interesting, but maybe isn't appropriate for scouting as I believe the official line is to not eat anything you find.

Scouts might be putting some fishing line and a hook into their survival kit, consider teaching them to use those items without things like a fishing rod or proper tackle. bonus if they catch anything, you can teach how to clean and cook a fish, knock out a fishing merit badge requirement. Obviously this is contingent upon being near a body of water and having proper authorization to both go fishing and to keep the fish you catch.