I am an electrical engineer. I would not worry much about the lead used in solder. Just don't eat anything. Most electronics should be safe from a chemical aspect. A shock hazard perhaps.
You are not going to find much in the way of magnets unless you have something with an actual coil speaker or motor. A modern day phone probably has a piezoelectric speaker. No magnetic material in those. Transformers will have some ferrous material in them that may have a small magnetic field to them.
Most ferrous material (iron) has a weak magnetic field. I have heard of inserting a needle through a cork and floating it on water to make a compass.
Many buttons, e.g. T.V. Remotes and older calculators, have lodestones in the plastic buttons. They were used to close circuits without worrying about narrow guides that would wear away after repeated use. Those little buggers have pretty weak fields, however, and make for terrible compasses.
Brian depending on where you live there are some great older boy camps around. My son and a friend went to Camp Rainey Mountain in Georgia last year and did a week of whitewater rafting camp. CMR shares the program with Camp Woodruff. Both are in northern Georgia not far from the Smokey Mountains. It was a 10 hour trip each way and they weren't the scouts from the furthest away. There are aquatic bases in a couple of the northeast states too. Just about every camp with older scout programs allow scouts to come as provisional campers (you don't have to go with your troop or own adult).
Here in the Great Lakes State, there are backpacking camps offered at Pictured Rocks National Lakeshore on Lake Superior, ATV camps, horse trek camps, canoeing and kayaking camps along the many rivers in the state. And sailing adventures in Straits of Mackinac area. Philmont has individual treks available for interested scouts. Sea Base has a match board for scouts that want to go but have no troop to go with. Not sure if Northern Tier has a similar thing.
What I'm telling you is you don't have to be stuck with your troop at the local minimalist summer camp. Read the ads in the back of Boys Life and research a place to go. That's how my boy found CMR. The sky's the limit.
Since oldest has been in Scouts, only 1 of the 3 camps he went to had any free swim or boating during the day. One had free swim as a nite activity, but no boating. None of the camps had free shooting during the day, 2 only at nite, and one of those limited to shotgun OR rifle shooting. Son still has a partial in Archery MB.
Additionally you would have some Scouters protest. One SM thought one of my Scouts wasted his time taking Swimming a second time.
I am not an engineer, so I cannot tell you about nasties and what not. BUT, my sons dismantle old electronics all the time. Computers, iphones, HO scale engines, you name it,they probably took one apart. So far, so good.