What Home Improvement Supplies Are Worth Buying in Bulk?

I’ve been looking at ways to make home improvement projects more efficient, especially when several properties or renovation jobs are involved. Buying commonly used materials in larger quantities seems like it could save both time and money, but I’m not sure which products are actually worth purchasing this way.

For contractors or property managers here, how do you decide what to buy in bulk? I’m particularly curious about less obvious maintenance and safety products. For example, I recently came across Wholesale radon supplies while researching ways to handle indoor environmental concerns, and it made me wonder whether products like these are normally purchased individually or in larger quantities for multiple projects.

Are there any home-improvement or building-maintenance supplies you’ve found particularly worthwhile to source in bulk?