At a time when gas prices are on track to top $5 a gallon, about 100 volunteers for the Meals on Wheels program keep showing up for their next car full of deliveries at the Modern Maturity Center in Dover, where the program is based. The center offers reimbursement money to drivers, but at 55 cents a mile, it isn’t enough to break even. For volunteers who don’t need the money, that’s fine. But for others, their ability to volunteer is being increasingly jeopardized by the ever-growing prices at the pump.