To enable Flare highlight it but do not throw it down.
Press Left or Right when it is low and highlight another object then highlight Flare again and it will have restarted and you will not lose another one.
Blood Test Kits -
To gain the the trust of your team save Blood Test Kits to show them your are not infected.
You cannot use them on a team member because they get infected randomly and usually break out within a minute of infection.