If tickets or memorbilia are on thermal paper (overseas you get that alot) I photocopy them. If the paper is really thin and flimsy and I don't think it is going to last, I photocopy it and use the copy in my books.
For menus and take-out menus and things like that, I photo copy them so I know they are on a good quality paper.
The original stuff I use is always sprayed lightly, front and back with a product called "Make It Acid Free" which is made by Krylon. So far it seems to be helping.
It can be pricy but a can lasts a while. My store just placed an order for me so I bought 3 cans.
I lightly spray the front and back - it dries in seconds. If you oversaturate the ink sometimes runs so use it with a light hand and it will be fine.
I don't like the results on glossy paper, as it puts a white film on glossy so I spray it lightly and if I see the film I wipe it off.
This is supposed to be good and I don't know of any other product out there to preserve papers. However, I haven't used it long enough to know how well it works, but I feel like it is better than nothing.