Should I use a combo sunscreen-and-bug-spray product?

Skip the combo products. Apply them separately because sunscreen needs reapplying every two hours, while bug repellent lasts six to eight hours. Combo products make you either over-apply repellent or under-apply sunscreen, and DEET can lower SPF effectiveness by a third. Instead, layer sunscreen first, let it dry, then apply repellent on top.