Ahh. Tuna "Helper" - Any kind of hot sauce goes well with tuna but I prefer Tabasco. In lieu of actual hot sauce, the Border taco sauce in the packets works in an emergency - the hotter the better (but I weed out the "will you marry me" packets, it just felt wrong to send those). The free pizza condiments I get in packets, and also work well with tuna, are crushed red pepper, parmesan cheese and "special seasoning". Soy sauce works with tuna but not the mustard or duck sauce (those are nasty).
If I get the feeling from a contact's updates that it's something they can work with, I'll send narrow, cylindrical containers (we have some here that fit perfectly between cans of soup) of basic spices including, but not necessarily limited to, lemon-pepper, garlic powder, onion powder, salt and pepper, and possibly a small bottle of Tabasco (wrapped very well).
Of course, all of the above also work for adding to various MREs.
Additional notes: The official recipe tester in my family will not eat the tuna and taco sauce combination but is quite fond of tuna with parmesan, special seasoning and a little mayo.
When I send more than a few packs of condiments I try to put them in a small box or plastic container to protect them in shipping. I sometimes have to kneel on my boxes to seal them shut and I'm afraid the packets will rupture or get punctured in packing and shipping.