How easy is it to tell needs from wants if you reside in a land of plenty (such as the US, Canada, the UK or places with all the modern creature comforts)?

When you live in a highly industrial area with many amenities and modern conveniences, how easy is it to determine what are true needs over wants? In other words, what are things desired that are truly needed to keep one safe, healthy and provides for basic survival as oppose to things that are can be cut out but literally makes living more convenient?