You can take tents and other shelters as part of your luggage allowance, as long as they’re packed in bags or cases under 85cm long.
Camping gas or butane cylinders and canisters cannot travel on trains according to SNCF/SNCB regulations, so you won’t be able to take these on board under any circumstances.
You can take camping cutlery and tools like pocket or Swiss army knives, as long as any blades are less than 3" (75mm) long. Any folding knife with a blade that locks is strictly prohibited, regardless of size.