I have a pretty spartan lifestyle. While some soldiers may need 400-500 / month spending money...I easily do with half. So, yeah, I'd rather mod out a Wrangler and spend my weekends trailing, hiking, biking, camping....
Pretty inexpensive lifestyle.
And to answer your question....10% in the TSP will suit me just fine!
Rough estimates for me (excel is your friend) put my Jeep at $31k with most fo what I want...and at E-5 it's manageable. I NEVER was one of those E-3's with a BMW that took half their paycheck!