One answer would be a federal sales tax, combined with a Universal Basic Income. The UBI would be equal to the amount of the tax on up to some minimum income l

One answer would be a federal sales tax, combined with a Universal Basic Income. The UBI would be equal to the amount of the tax on up to some minimum income level (say, 50k / year). In other words, everyone gets a monthly check that is essentially a rebate on their sales tax up to the income threshold. That's simple, loophole-free, and avoids the privacy invasion that accurate income tax collections require.