The material is likely the most important aspect of buying fasteners, bolts, and screws, and the only logical thing to do would be to go all out on metal. Even though that is indeed the case for fasteners, bolts, and screws which are often going on and off the car, a more affordable material can also be acceptable for less important and lighter ones.
Another really important aspect is whether you are using your fasteners, bolts, and screws outside or inside. Some materials such as 316-grade stainless steel are more resistant to outdoor environments with more moisture while cheaper 18-8 grade steel is more than enough for dry indoor environments.
There are many different types of fasteners, bolts, and screws to choose from such as bolts, screws, nuts, washers, rivets, rods, clips, pins, and a whole host of different screw heads and nut types. The most important thing here is to know exactly what you need beforehand so you don’t have to spend time trying to understand why something does not fit properly.
Last, but certainly not least, we also need to talk about weight. Using heavy-duty screws on something like a plastic inner fender is unnecessary while using plastic screws on heavy-duty spare tire holders is borderline dangerous. As such, go for larger, more capable hardware if the object you want to fasten is heavy, and go for lighter hardware if it's lightweight.