Use Muc-Off, buy it when its 'on offer'. No snot balls like Stans above, easy to clean up as well. Injects through Presta valves with the core removed with a tube over the top of the valve so easy to use.
I use muc-off, in fact yesterday, and it didn't work. It did inflate the tyre but didn't keep the puncture closed long enough to get home without a fecking long cold walk. I didn't remove the presta valve core though, is that what I should do? Makes sense now I've read it, but out on the ride covered in wet cold mud the brain doesn't work that well. Also people are mentioning "topping up" what does that mean? Are you pre filling the tyre before getting a puncture. Sorry for all questions but I get shed loads of punctures, I'm sure farmers plant specific pointy plants to put us off