Thanks for feedback. I will replace text in the UI to icons to make it more clear. As for now I can give explanations on what the text means.
O2 is you oxygen. It goes away and keeps you moving. Picking up O2 ballons and bubbles will refil it.
RE is Reactor. Gives you tmporary speed increase and is very usefull against final boss.
RC and MI are counters for Rockets and Mines.
There is an upgrade that increases your speed a little. Just above unbearable I hope. It's on a main path so you won't miss it.