What can I use instead of top coat?

What you can use instead of top coat depends on project, but there are alternatives that provide similar protection and finish. For interior house walls, if you don't have top coat paint, you can use self-priming paint and primer in one with two coats as top coat, or use leftover paint of similar sheen, as primer alone is not washable or durable. For wood furniture and trim, instead of polyurethane top coat, you can use varnish, lacquer, shellac, Danish oil, tung oil, or beeswax polish for protection, each gives different sheen and durability. For floors, you can use hardwax oil instead of polyurethane. For cars, instead of automotive clear top coat, you can use 2K clear coat spray, ceramic coating, or wax as temporary protection, but clear coat is best for gloss and UV protection. For nails, instead of dedicated top coat, you can use clear nail polish, which adds shine and protection, though not as durable as gel top coat. For crafts, instead of top coat, you can use Mod Podge, clear acrylic sealer, or epoxy resin. So alternatives include other paints, varnish, polyurethane, lacquer, wax, oil finishes, clear nail polish for nails, and ceramic coating for cars, but for best durability, use product designed as top coat for that surface.