Milton Fluid and probably the denture-tablets mentioned above are just very dilute, simple bleach (calcium hypochlorite)! Same as water-purifying tablets.
Magnets: my " Magnets, 'Fridge & gen. Purpose ", are from scrapped hard-drives, and are quite powerful.
The pumps that come with liquid soaps are very good for decanting small amounts of liquids from full 5l cans of the type designed to throw the liquid everywhere if simply tipped. (Those typically used for wood preservatives, etc.)
Scrapped IT equipment is a handy source of precision steel bars (in printers), circlips, thin-gauge sheet-steel, self-tapping screws….
For cleaning my Myford 7's chip tray, an old paint-brush with a child's toy plastic beach spade, short-handled, has proven ideal. A long-handled equivalent with a steel blade (that dates it!) is there for anything from rooting swarf out of corners, to planting small shrubs and clearing the visiting cats' offerings from the lawn – and yes I do clean it after the latter, by digging a patch of bare earth!
A small irritation, I found the bed under my Harrison's L5 head and tail stocks would fill with filthy swarf. I cut two simple covers longitudinally from off-cuts of ordinary (60mm?) plastic rainwater-pipe, to slide under the shears.
Extra protection for the armoured cables on the Machine-DRO read-out sets: the plug and the sensor won't go through ordinary flexible PVC electrical conduit, but the sensor does pass through a similar tubing about 30mm dia, made for caravan plumbing. It's surprising what useful materials come from unexpected places like caravan-site shops!
Old plastic bank or association-membership cards: cut off embossed areas, and the rest is useful shim material. Some at least are also a suitable thickness for a mid-gap range, non-magnetic feeler-gauge for setting the magnetic-sensor gap on the above-mentioned DRO.
Workshop calculator or similar, or your 'phone? Keep it clean in a polythene, e.g., freezer, bag.
Slide-way cover: The original cross-slide way cover from my second-hand Myford VMC mill having long departed hence, I have replaced it with one cut from surplus garden-pond liner. I don't know how long it will last but it's holding up so far. The upper clamping strip was lost too so I used a length of thin aluminium-alloy angle, which also creates a narrow shelf in which a few holes of various sizes hold small items like the drill-chuck key and wobbler.