You can take pretty much what you like. The X-raying is looking for bombs rather than being airline style, it's more like airport X-rays used to be before all the liquids nonsense etc.
The only things I can think of of note is that you can't take camping gas cartridges (LPG is not generally allowed in the tunnel, even I think LPG cars), knives that are non-folding or over 3in blade (this sounds like it wouldn't be an issue but would include I think regular household cutlery as you may want to take if camping, so if camping best take a plastic spork or similar instead) or hot drinks other than in sealed flasks (because everything goes through the X-ray machine and they would spill, you can buy them "railside" though).