"What to do when you live in a shoe"

What to do when you live in a shoe isn't really a "popular saying" across the world at large. Google finds only 31 instances of this quotated text on the whole of the Internet, at least half of which are simply duplicated references to the same original instances.

A related but far more common expression is living in a shoebox, meaning "in a small appartment". This probably owes much to the nursery rhyme There was an Old Woman Who Lived in a Shoe who had so many children, she didn't know what to do.

OP's (possibly quite localised) idiomatic usage seems to convey a sense of making the best of limited resources. I'm assuming when he gives this reply to someone asking why he doesn't have fast broadband, it's because he lives in a rural location where fast connections are unobtainable or prohibitively expensive.

My own guess is that OP's meaning has arisen circuitously from the original nursery rhyme context. Apart from lacking access to modern contraceptives, the old woman was probably poor, since people living in rural locations are on average poorer than those in the city.

When it comes to broadband, the economics become even more relevant. Even if you live in a tiny apartment in a city, you can probably get cheap broadband because the cost of wiring up the whole building become insignificant when shared between all the people living there. When you live in a farmhouse miles from anywhere, the cost of getting connected by cable can be astronomical.

I've heard the phrase as "what can you do when you live in a shoe?" myself. Perhaps you'll find more hits there? I learned it in rural Ontario and it has the meaning you indicate, accepting what you have to accept. Rhyming is definitely part of the idiom. In my youth, people would indicate they agreed with your sentiment by replying "and you can't dance." Perhaps this was the first line or two of a poem or song?