Like you RosiesMaw, I grew used to doing things on my own during my husbandd's last illness, and as my friends in the area where we chose to spend our retirement don't share my liking for classical music and ballet, I usually go to concerts or the theatre alone.
Nor does it worry me to join charity walks or the like on my own, and doing so, like you, I have found it is much easeir to chat to strangers than it is when accompanying a friend.
Often I make a conversational remark about the activity or event, or even the weather, if I am standing at a bus-stop, if the person I address doesn't seem interested, then I take the hint, but as often as not, I find myself having enjoyable conversations this way.
I don't drive, so I cannot advise on the problem of a friend wanting to share the driving - but is honesty not the best policy here?