What does Spoil Yourself Silly on a Shoestring mean? It is the title of a chapter of the book I'm reading.
Why not translate it part by part:
From Oxford Advanced American Dictionary:
silly in such contexts means so much.
The sentence means make yourself happy by using very little money many times, don't use all of your money at once.
To spoil yourself is to treat yourself, like a parent who buys too many toys and sweets for a child.
Silly here means to do it excessively, the idea being you would do it until it makes you silly.
On a shoestring means on a meagre budget.
So the whole thing means "Treat yourself excessively on a budget".