I live in my employers service area and am 5 miles away from the base (2 miles, if we end up moving one of the older ambulances to the fire station), and I often respond to E1 priority calls when I know I can get there before the ambulance, or if they may need an extra hand (cardiac arrest). Also, sometimes if we are out of service, dispatch will call for QRP because the nearest bus might be greater than 10 to 15 out.
I used to respond to every E1 or E2 I could (E3 is toe pain), but quickly realized other than getting a history and vitals, there wasn't much I could add to (the medic is going to get their own history and vitals anyway). These days, I rarely respond unless it's a good one. There have been a few instances where we've been able to have one person QRP to the scene, and the other grab a bus from the station and meet on scene, which means keeping our own calls, instead of having the other service get them, but that only happens if a few people happen to be listening at the same time.
We get 1 hour of pay if we call en route but get cancelled, 2 hours if we get on scene and assist, and 4 hours pay if we ride in.
That said, I carry gloves, a steth and cuff, several gauze pads, hot/cold packs, some tape, and a BVM. Might add a tourniquet but not really in a rush to get one.
The most used items would be the steth and guff, I've used the 4x4's once (with tape), and took my BVM out of the bag once, but didn't use.