Assortment Kits

Search auction sites for 'assortment kits' and you will find plastic boxes full of a variety of hardware and other equipment.

List of useful assortment kits from local or chinese manufacturers

Good Assortment Kits

* stand offs (m3 seems like a good start. m2 is likely a bit small)(stand offs are always expensive)
* small machine screws. (microcenter has a small box of these for like $4.
* washers (i like the huge washers, they are called fender washers) (these are not cheap), also lock washers (not spring washers which even nasa does not like according to https://en.wikipedia.org/wiki/Washer_(hardware))
* Heat shrink tubing (clear is great, but 3:1 type, not 2:1, is the high end type).
* 1000Pcs Micro Screws Nut Electronics Assortment Kit for Glasses Watch Cellphones
* Threaded Inserts
* Anchors - Some of the assortment kits are bad, but the anchors have been good. It's hard to get plastic wall anchors for mounting things in the wall wrong. 

Just search for "assortment kit". don't ever buy the kits that are in the shape of a circle. those won't stack well in the cabinet.

Keep in mind, some items may be of poor quality. The idea is that these are cheap and ready for quick work. Not to be used in production items.

Harbor Freight stocks a few of these assortment kits. They may be scattered across the store.

Bad Assortment Kits

* crimp connectors - You don't want to play around with crimp connectors. I have gone with what EEVBlog Forums recommended which are the TE Connectivity (Tyco)