I use various things. Old canes with tennis balls on top to save the eyeballs and a name label tied on. The small square section bits of wood used as spacers at the fencing suppliers for piles of stobs (they are just chucked out with the rubbish normally so no-one objects to me collecting them), name of crop painted on, reuseable year after year. Hazel poles which are too short to use for beanpoles - shave a smooth flat bit on one side at the end and paint on name of crop. If I had field length rows old fence stobs could be used.
For seedlings, I'm lucky enough to have a 'Brother' label printer, which I stick onto plastic labels (which I bought years ago before I cared about plastic use) - they can be peeled off each year so I don't buy new plastic, but you could use recycled plastic from spread tubs or milk cartons. The labels last several years before the print fades, unlike pencils and marker pens which photodegrade before the season's up. I sometimes tie these labels onto sticks when the seedlings are planted out.
There are so many things you can use, depending on what you have lying around or growing. I no longer buy new canes from China as I grow coppiced hazel and willow which provide much more attractive poles and sticks.