As part of a national sales tax, it would not be imposed upon necessities... Such as food or clothing, among other basic necessities. Alternatively, take your "prebate" and give everyone a $5000, or whatever amount of exemption... For example whether you make $25k/yr or $1,000,000/yr you get a prebate/rebate for the first $5000 of federal sales tax you spend. Either option, but not both, is a simple solution to ensure that ensured people are not taxed on the minimum to get by but only on luxuries.
The complaints about this being "regressive" are exactly why the truly fair and equal plan would be better. Everyone pays their fair share, divided evenly among everyone. Very simple.