You could quite possibly sue for your money back, but that is the very opposite of being economically worthwhile--even representing yourself in small claims court, you'd spend more on the filing fee than the food cost. The problem is, if you are lucky enough to have not been injured by the band-aid--e.g. you did not contract some illness; you did not break a tooth on it; you did not choke and  either suffer injury and/or have to pay for  medical care--there is nothing to sue for. The legal system provides compensation for injuries or costs; no injuries or costs, no compensation. Merely being disgusted or "grossed out" would not provide grounds for recovery or compenation, unfortunately.