I ask because whenever it is a hot day, the sylphs in the area send nice breezes where I am if I ask them to. This could probably because I thank them whenever they send a breeze my way.
So my question, is thank you gift enough for them, or is there something more i could give them to really show my appreciation and gratitude?
Gratitude and appreciation are generally enough, but if you want to give something more specific, you could give an offering of incense. Any pleasant scent would do.
They like shiny things: crystals, zirconite or glas and flowers, lots of colourful flowers. Also tiny melodious bells and bellringing
Agrippa lists minerals, herbs etc. related to Mercury, the air planet; anyway, included between them or not, an example is cloves.
So I gave them a goldstone cube as a gift and holy crap, a huge breeze of cool wind showed up out of nowhere and I heard thank you through telepathy from the sylphs.
Oh, that is delightful to hear.