I know there are a lot of purpose-made boxes sold for storing coins in cardboard holders, but I think a lot of them are deficient, if only because they'll allow contact between the staples on a holder with a small coin that's against a large coin that could end up next to the small coin. Yes, the staples should be flattened, but they're still there, unless you use staple-free holders, potentially damaging that larger coin.
Personally I think photo slide storage boxes are a much better choice. They're designed to hold those old school photo slides (if you're under a certain age you may need to search for what those are) apart from each other just a bit. Those slides are exactly the same dimensions as standard cardboard coin flips. The way they're held in the boxes also allows me to read the information along the top of my cardboard holders so if I have a range of coin varieties in there I can see from the top which are which. I write coin type along the top of my cardboard holders.
These boxes can usually be found for remarkably little money at auctions, estate sales and secondhand shops, as can slide storage pages, which are pretty indistinguishable from coin storage pages used in two/three-ring binders.
This is perhaps already widely known, but I hope a few people will find this information helpful.
This style of box is nice, as it is quite portable with the little handle. You'd normally lay it flat on the left or right side as you're looking at it and raise the lid on the other side while the down side is latched shut. If travelling any distance I'd put a little strap around it to ensure the contents wouldn't spill out if the latches got opened unexpectedly. This one will hold 350 coins.

This type is less suited for travelling. I don't have it in front of me, but I believe it holds 100 coins per tray, and the trays slide out. The cover is friction fit.


This is a small box designed to hold about 20 slides/coins, although it doesn't have anyway to keep them apart from each other inside. It's just something I came across in a box of larger slide boxes and realised it's handy if I'm travelling and just want to carry a small number of coins easily. Conversely, I often use just a single slide page from a notebook and put it inside a letter-sized folder/notebook. But this is also handy if you want to carry them in a pocket.

Do not read this sentence.