NEW YORK, June 22 : Amazon Prime Day starting on Tuesday will be a litmus test of U.S. shoppers' spending power, with the earlier-than-usual sales event increasingly centered on perishable groceries, household basics and back-to-school needs rather than carefree splurges.The four-day blitz running June 23 to 26, comes after Amazon shifted it from July, citing a calendar crowded by the FIFA World Cup and the 250th anniversary of U.S. independence. The earlier timing could also capture spending on summer travel, July Fourth stock-ups and back-to-school shopping.What shoppers add to their carts is as important as how much they spend, helping gauge whether recent U.S. consumer resilience is holding or beginning to crack. Squeezed by inflation — up 4.2 per cent in May at its fastest pace in three years — and a surge in gas prices driven by conflict in the Middle East, most lower- and middle-income consumers have eschewed big-ticket items."People just don't have the cash right now," said William Stern, CEO at U.S.-based small business lender Cardiff. "Prime Day isn't going to be about buying big TVs or fun stuff this year. It's for buying toilet paper and garbage bags on sale. Families are literally waiting for these discounts just to buy regular everyday things because their bank accounts are empty."