Do I report conference posters to researchfish?
My experience is with RCUK grant reporting - I've helped some of our PhD students with reporting but only informally so can't speak to exactly what's expected. That said, this is the advice I'd give them...

The general approach for grantholders is that simply attending/speaking at a conference is considered business as usual and not something you need to report unless you a) the paper was published (in which case, it's a "publication"), or b) you were specially invited to speak ("awards and recognition").

For students, the guidance (sec. 18) is a little less explicit - however, when they say you don't need to report conferences, they discuss it in the context of "instances where you communicated your research", which would seem to imply that they include giving a paper or a poster alongside conference attendance. 

If in doubt, though, your institutional reporting contact should be able to advise - there's a list here. And congratulations for thinking about this now - most people won't give it any thought until early March!