PMK is nearly immortal. Stock solution lasts many years (at least six in my experience). It works best on non-T-grain films in my experience. I use it about 90% of the time on such films. Caveat: it contains pyrogallol so one should wear gloves while using it. The staining it causes on negatives makes them easier to print, in my opinion, since the stain is proportional to image density.

Rodinal is nearly immortal too. It's grainier than many developers so I don't think it suits all films, but for some it's terrific.

HC-110 is quite long-lived. It results in lower quality negatives than XTOL or D-76 do but it's very convenient. It's more suitable to T-grain films than PMK is.

Another option is to switch to something simple like D-76/ID-11, that you can mix from scratch. That way you can mix up the exact quantities you need, e.g. 2 litres for the next 3 months. It can also be bought in one-litre packs but costs more this way than mixing from scratch.