sales tax is inherently regressive which is why a lot of states, but not all, exclude food and clothing from sales taxes to minimize the regressive aspect to discretionary spending, so the real crossover for the discussion is what level of spending should be considered non-discretionary.
In my mind, food and clothing are so cheap it almost doesn't matter that they are taxed. We have AFDC, WIC, etc to help people with dependents. Even if paying for food, big bags of frozen vegetables and soup stock are cheap. $10 a day will easily feed an adult.
I might spend $300 a year on clothes, and I feel like it's less. Some $15 jeans, a few "outlet store" shirts and pants. Socks and underwear from the "Dollar Store". Coats from Goodwill. Mail order some nice shoes every 3 years, and augment with some cheap sandals at Wal*Mart once a year.
I think what's great about sales taxes (and property taxes) is that you can control and manage them. Heck, many necessities (kitchen items, yard tools, furniture, baby goods) can be had for free - if you just ask for second hand items from friends, neighbors, family, your church.