I think just sling them into the scrap bin mate. If you've had them kicking around that long, then you are never likely to need them!
I use a lot of screws, bolts, nails and other fixings and the ones that have come with furniture and stuff, as free gifts (multipacks like those from tool/building companies) or from other folks' random tins are the ones that never get used. If I need a screw, then I need a certain size/type and I go to the box full that I have bought, not search through a bunch of pots and draws. Also, the screws that come in those multipacks are always awful quality and shear before being driven home or the heads turn off straight away (if they even fit the drivers properly to being with!). I've got boxes (totalling about 15kg now) of imperial sized machine screws sitting around, and they do occasionally come in handy for repairing old machines, but mostly they are glaring at me from a corner
N.B The idea of 'just melt them down and make a knife' gets thrown my way for all sorts of things, and it is rarely if ever a sensible suggestion I'm afraid folks. Firstly, they don't melt: steel is forgewelded in the solid state, not like bronze. Secondly, screws are normally coated with zinc and other corrosion resisting substances (hence the yellows and greens you often seen); these stop things from sticking together and likely not very good for your health if you heat them up. Thirdly, if you do a canister type set up to weld any uncoated screws, then you will likely need to fill the voids with some powdered steel (which is ruddy expensive in the UK) and the whole process would be far more expensive than the results would be worth for a lump of rubbish steel.