Most states would just recreate the food stamp program at the state level, as it is one of the more effective welfare programs, despite its shortcomings. Plus there will be pressure from grocers and the like to keep it.
And without very specific and guaranteed guidelines and restrictions (which would render block grants pointless), they'd likely create variations of that program that are much harder to qualify for and maintain. You should see how difficult it is to qualify for Medicaid in Georgia and other states following the bare minimums; hopefully, you're a pregnant female with 12 dependents and make $5 per year, because that's about what it takes. The federal minimums are ridiculous for it, as they'd likely end up being for SNAP et al.
Variability in qualifications for Medicaid have to do largely with the fact that the states have to contribute between a third and a half of the total cost of the program out of their general budgets. If states are getting money from the feds specifically for the administration of antipoverty programs, the tendency would go more toward getting your money's worth. That's not to say there wouldn't be constraints on the programs out of ideology, but the financial and political incentives would be different. On the other hand, one snag you would expect with block grants that you do see with Medicaid is the distribution formulas to the states, which often do not correspond to actual need.
