A July 2011 report from the Bipartisan Policy Center assess what happens if the U.S. runs out of money. It reports, for instance, that if the government chooses to pay…

Interest on Treasury Securities – $29.0 b
SocialSecurity Benefits – $49.2 b
Medicare/ Medicaid – $50.0 b
Defense Vendor Payments – $31.7 b
Unemployment Insurance Benefits – $12.8 b

Then it could not pay for these programs:

Military Active Duty Pay – $2.9 b
Veterans Affairs Programs – $2.9 b
FederalSalaries + Benefits – $14.2 b
Dep. of Education (e.g., Pell grants, special ed. programs) – $20.2 b
Food/Nutrition Services + TANF – $9.3 b
Dep. ofLabor (e.g., training and employment services) -$1.3 b
Dep.of Justice (e.g., FBI, federal courts) -$1.4 b
Dep.of Energy (e.g., energy research, national nuclear programs) -$3.5 b
Health and Human Services Grants -$8.1b
Federal Highway Administration – $4.3 b
Environmental Protection Agency -$0.9 b
IRS Refunds – $3.9b
Small Business Administration – $0.3 b
Federal Transit Administration – $1.3b
HUD Programs(e.g., housing assistance for the poor) – $6.7b
Other Spending -$52.8 b