Here is a trick I've been using for years. Yes, there are the transparent envelopes and yes, most Filofaxes have side pockets too, but I still used to find that tickets got lost or forgotten now and again. What I now do instead is punch an envelope and file it in the diary section between pages containing the relevant date. Using a tiny envelope (they come in packs of 50 from WH Smith) works really well:
The tickets are tucked inside. Depending on where you punch the holes you can access them without opening the rings, too:
Here's another method using a more conventional envelope. This one is a C6, too big to use in anything smaller than an A5 Filofax. But we're going to modify it. First, we'll cut off the end:
Another small cut to tidy the flap, and then we can punch it:
And here it is sitting in place in the diary:
You can also try this using one of those transparent CD envelopes, but I find they don't react too well to punching.
The joy of this method is that you can accommodate tickets of almost any conventional size and have them to hand precisely when you are going to need them.