Today marks the end of the federal government’s fiscal year. It’s also the biggest one-day shopping spree of the year– the day when federal agencies rush to spend the last of their money before October 1, before anything left over is returned to the Treasury. Since agencies cannot carry over unspent funds, the idea is “use it or lose it.” If they don’t spend the money, Congress may not allocate as much the following year. Last year, the government spent about $50 billion the week before October 1, according to NPR’s Shankar Vedantam.