A ring basket that can be put around flower stems to help them stay upright, but small enough to be inserted into a vase. Often cheap flower bouquets achieve this with a rubber band, but poorly -- this is a reusable solution that does a better job.

Included is the underlying OpenSCAD file (depending on BOSL2) which can be adjusted to different size parameters. It's rendered with 16 facets due to size contraints -- 100+ is possible for a smoother circle, but the STL file can easily grow beyond 1GB.

PETG

Probably any filament works here, but I think PETG holds up best underwater.