I don't! I am financially well off enough to buy what I want when I want to however I'm able to do it with some 50 years of having worked and made sound investments, mostly stashing coins and dollars away in a safe box I keep in my house. And of course my retirement money I get each and every month. I have been very good at saving literally pennies and more over the last 50 years to get myself in the position I am in today.
So I don't feel a need to justify what I spend on any hobby I may have or anything else I may want.