I'm a single mum with a medical condition and a 5 year old son. It's very unlikely I'll have a problem but I feel much more confident being prepared!
My doors are very stiff and the windows don't open much - it's great home security but I don't know that my son could escape! I bought a landline phone and we call it my son's phone. I programmed his dad, my parents and my ex in-laws into the speed dial and have encouraged my son to use it a lot so he is comfortable with it. He also knows about 999. I don't know your DCs ages but a landline phone could be worth thinking about. It means he won't need to find or unlock my phone and speed dial can be quite easy and fun for kids. Phone calls are included in my line rental unless they go to over 100 minutes or something. I have been teaching my son his address and my name in case he needs them for 999.
He has access to a shelf of snacks, the fridge and fruit at all times, but again I know this is harder for younger children. When I worked in a nursery, Ofsted loved to see 2 year olds serving their own dinners and getting confident with food - it is a good thing to aim for a bit of self-service even from a young age.
I have a key safe outside the home and a couple of people know the code.
I have routines that people would expect me to be at but if I didn't, I would set up a weekly text check in with a friend. Be honest and say it makes you feel safe, people like to feel needed and it might help you both a lot.
And get to know your neighbours! Introduce yourself, bring them cookies, have them in for a cup of tea, it could help you feel a lot more comfortable.
Honestly, making some small adjustments has helped me feel a lot more confident and in control. I would recommend it.