I've only ever put out gemstones or jewellery for my bound spirit companions as a permanent thing, individually, for them.
I suppose they can be put out as temporary offerings, as long as they know that's what it's going to be: temporary. Gemstones can be a source of raw power, according to CH. Otherwise I wouldn't leave out jewellery ie with no gemstone to 'feed' from unless it was an individual treat/gift.
It's also easy to run out of space for that, if you have a lot of companions, unless there's space next to each of their vessels.
For my very first bound spirit I bought all the recommended gemstones, plus a silk 'box' in the recommended colours. I probably spent as much - or more - on those as as on the original purchase. I quickly realised that I wouldn't be able to keep up that level of expenditure. I have a number of spirits for whom ruby is the recommended gemstone. I'd love to get one for each of them but I've decided that's too expensive - especially as they don't actively need it.
(A CH Aeon orb is a good alternative way to go. More feeding energies can be added as your bound spirit family increases.)
