Muscle electrode stickers are not re-usable (that's why we burn through them). Patches can be used only once or twice until the built-in gel loses its "stickiness" and its purpose. So, it really depends on how many times you're going to do the experiments and how many people will be doing experiments. But it's always good to have more stickers. 

The same goes for the Electrode Gel. When you're recording EMG from your small muscles, with small precise muscle electrode sticks, usually you won't need any more gel than that's received in the package.
When you're doing a lot of EEG or P300 experiments with your Heart & Brain SpikerBox, then it's a good idea to have a spare bottle of gel.
When recording from the plant, we'd say one bottle is plenty! 

If you need refills, you can order from our website: 

Large Muscle Electrodes (100 EMG patch electrodes)

Electrode Gel