I don't know how they could have installed a new chain without removing the front engine cover/s. Check you records for a list of parts replaced. You can replace the chain by removing only the right valve cover if the chain is intact. Once it breaks, there's no way to thread the new chain unless you're so lucky that the both ends are in the area of the cam sprocket. Even then, you probably have to take the front of the engine apart to make sure all the sprockets are aligned.
A head gasket set should have everything you need. On the earlier M116, the left and right head gaskets are different. They are probably different for your engine as well. Make sure the head gasket set includes a valve cover gasket.
Any other parts will depend on what you do with the head and what was done with the timing chain. If you have the done as you probably should, it will be ready to install. If you don't have the head done, at least replace the valve seals. Check the plastic fittings on the oil lines above the cam towers. Check the chain tensioner and guide rails. If they were replaced when the timing chain broke, they should be in good shape.
You'll have good access to the water pump and the various coolant hoses so consider their condition.
If your engine is anything like my older M117, keep track of the vacuum hose behind the throttle body. There's no way to reconnect it with the intake manifold in place.