On my midnight commute home on country roads I'm unlike to see a car the whole journey, and there ain't no mobile phone signal for some of it on any network. I hurt myself, I'm on my own, and even if I could summon help I'm not likely to get it in a hurry out there.
50% of my old 15 mile commute, one I did for 7 years before going off on a RTW tour, was not even on roads (single track or otherwise), going across an MOD training area and 2 nature reserves. 99.5% of the time, I would not meet anyone at all even during daylight hours. It was unlit, overgrown and subject to being very wet, muddy and difficult anytime it rained with trees frequently fallen across my route. I lived rurally with no neighbours, when my husband was away, him checking I had arrived home at night ringing our landline was the only way anyone knew I was home safely. There was no mobile phone signal at home and none at work either. Needless to say anywhere inbetween was not covered either. I did not even bother carrying a phone, in fact did not have one. I was on my own. This was rural Surrey/Hampshire border area. (For reference: I have lived in some of the most remote places in England & mainland Scotland where medical help is often hours away after being able to summon it and usually arrives by mountain rescue, not ambulance. I am used to being self sufficient.)
My point is that plasters are not going to be enough if you are needing that much help - it is better to have the knowledge to improvise; a sling can easily be made from clothing and commuting, that is something you usually have available even if it is only the dirty stuff coming home. Wounds can easily be washed out with water carried in a water bottle, and letting a small wound bleed is often the best way of cleaning it out. Personally I never commuted without full waterproofs being available to me - something that comes from my mountaineering, so combined with my work clothes (assuming I was carrying them), I had warmer clothes available, I had waterproofs available, I would have water to wash any wounds clean, I would have clothes that could be used for a sling, an inner tube for a tourniquet, an inner tube that could be used to stabilise a broken leg with the aid of a branch off a tree wrapped in clothing to make it more comfortable or even help stabilise a fractured pelvis if you got really creative(!) If you cycle in shoes with laces, tying them together will help stabilise a lower leg fracture as well - otherwise use that innertube cut in half to tie around your shoes. I would have some food & water with me and could easily support myself for 12 hours or so if needed by which time someone would have noticed I was missing (dealt with by my husband ringing me each night at a certain time when he was away from home). It would not necessarily be an easy 12 hours, or comfortable, but unless there was a severe frost due, I could survive (having completed a couple of survival courses helps just a much in those circumstances).
A standard first aid kit would not make much difference. What would you carry? A
typical pocket first aid kit contains the following: 1 x Primary Care Leaflet, 1 x Tweezers, 1 x Scissors (5.5cm Blade), 6 x Safety Pins, 1 x White Open Woven Bandage 7.5cm x 5m, 1 x Crepe Bandage 5cm x 4.5m, 1 x Savlon Antiseptic Cream (15g Tube), 5 x 4-Ply Gauze Swabs 5 x 5cm, 1 x Micropore Tape 1.25cm x 5m, 3 x Hygienic Cleansing Wipes, 1 x Low Adherent Dressing 5 x 5cm, 1 x Pack of Assorted Plasters.
How much use is any of that if you can't hold your hands steady from shock? How much is of use if you have a head injury and are confused? How much is of use if you have come off your bike and have an open fracture of your lower leg? Nicities, nothing essential.
The truth is that what you are probably already carrying as part of your commute will be just as much use keeping you warm and if you have no mobile signal, keeping yourself alive until someone does notice you are missing and sumons help.
I cycle in all weathers; this year in -15C in some remote Turkish mountains when my husband and I both needed help, not a single thing was of any use, in any of our first aid kits other than to cover my wounds to prevent frost bite something we could easily have done with clothing or a towel if needed - warmer layers of clothes & waterproofs, hats & gloves, water, food and my sleeping bag were of significantly more use, plus the straps that held our tent to the bikes to make a tourniquet. (My husband's injuries were left to bleed and not even covered - correct proceedure for his bite.) It was almost 2 hours before the first medical help arrived & 4 hours before I was seen by someone qualified to deal with an injury such as mine. I had a severed major artery, a punctured major vein, a severed major nerve and 1/3-1/2 of the back of my calf hanging off my leg amongst other issues. Of what we were carrying, nothing was big enough to even start to cover a wound that big. Cleaning the wound out, allowing it to continue bleeding a touch, dealing with shock and fluid replacement and staying warm in -15C with my blood freezing on the road was much more important. Ironically, that injury could just as easily have happened on my old commute though not necessarily from a dog. I doubt I would have got medical help any faster.
My point is that you are no worse off than before mobile phones when people relied on others noticing that you had not arrived and if you are that worried about it, you would be better off carrying something like a
Spot GPS messenger device (such as I have) that uses satelite to give your location and obtain help (subject to being coherent enough to find the devise and press the correct button). I can't link you to my review of it because CGOAB is down again at the moment, but that would be significantly more useful than a standard first aid kit if you are needing help to that degree. If you don't need help that much, then your wound can be cleaned with water and you get home of your own accord. Small standard first aid kits are not the answer, (IMO they are a comfort blanket, great til you actually need them, then you find their short comings), knowledge of first aid & survival is much more useful IMO.
When in the mountains, or far from medical help, we carry a
life systems mountain leader pro first aid kit (RRP £90) which we have added to. It's basic weight is 1.2kg and originally contained some 87 items; it now contains many more items. We are both trained to use all of the items and the truth is, that when we re-set out for more remote areas, we will still need to add more items to it. That is the sort of thing that would be useful, though you could probably get away with the smaller mountain version which only weighs 700g basic weight.