Why is this expression funny?

I have no idea! Is this brittish english?

I dunno. The joke is from this site:

http://www.monksofadoration.org/index.html

Nah - wallet would not mean travel bag, I don't think.....trying to figure it out....the shoeboxes must be assumed (for the joke) to be full of money.....hmmmmmmmmmm....

I don't get the joke either.

It's not British English..."playing catch" is not a British expression.

Maybe it's to do with some folk keeping money in shoe boxes, instead of in a wallet (Br)/ billfold (US) or in a bank.

Don't any of you have a male relative who has way, way too much stuffed in his wallet? And an extra bundle of credit/membership cards with a rubber band around it? And a drawer somewhere full of stuff that has come from the wallet?
Women like this just get an extra-large purse.
The joke is that the narrator is implying that instead of a wallet (a small thing that holds very little), 'dad' is using several shoe boxes for the same purpose. Needless to say, they aren't going to fit in his pants.

I finally figured it out -- out of context it fell flat, in context I get it but it's still weird.

They're packing for this trip, right? Usually that means suitcases, backpacks maybe, containers that are actually appropriate for transporting things. But the kid's dad has him packing things in... shoeboxes. Shoeboxes? Awkward, small, can't fit much of anything in 'em. It's almost as bad as if they were packing things in a wallet.

The kid's taking the silliness inherent in the situation -- using small, impractical containers like shoeboxes -- and exaggerating it further -- using a smaller, even more impractical container like a wallet. (About the smallest container one can think of.)

Does that make more sense?

Not such a great joke, but I can see how with the proper expression (long-suffering deadpan) and context it would get a laugh.

"Playing catch" btw is just two people standing some distance apart and throwing a ball (usually a baseball, can be a football) back and forth.

I think sozobe has inspired me, though not so much.

I am afraid the writer was not qualified enough to teach others with lecture like "How to Be Funny". Because even McTag could not get his humor.

Well, a whole lot of humor is context and tone. Comedians spend a lot of time setting things up. I can see how I would laugh at that line, in context, but out of context it's a puzzler. (And not that funny, to be sure.)

"Even McTag". I like that. It has a certain ring to it.

I think you're right. I don't find it funny and I was wondering about whether the "wallet" suggestion related to him being so "tight fisted" (mean with money) that he wouldn't buy proper luggage. I think Soz's explanation is better.

My advice - don't read this book if you want to be funny. In fact, don't read ANY book which proclaims to be the source of great witty comments. I tried looking a some when I had a "best man's" speech to do at a friend's wedding. Traditionally, this should be humorous but every suggested joke on marriage, etc. was either so old and over-used, weird or just inappropriate for someone I liked that I didn't use any.