Most dept. store blinkies I've used have been terrible. They'd start out nice and bright, but a few potholes will disconnect the contacts, and the blinky would basically cease working. (This happened to many LBS blinkies too, even not-so-cheap ones.)

Helmets, as others said, comply with the same crash standards. The main issue, imho, is fit - they're pretty cheap with a limited amount of adjustment. Ventilation is usually poorer as well. But if they fit you well and you don't care about the vents (e.g. you're picking a helmet for winter riding ) - they're just fine.

Gloves and things are probably okay. Cheap polyester sports shirts are about as good as jerseys for moisture-wicking and about five to fifty times less expensive.