Hi there!!
I think it helps to remember that you can stay very relaxed about solids. First of all, you are not likely to have him on 3 meals a day right away. It often takes several weeks to work up to 3 meals. During that time, his A time will likely get longer as well, so you will find you have more time to fit solids in around outings.
Secondly, most of the time you can come up with something to take with you. I would usually aim to do milk feeds at home where there is less distraction, but take some kind of solids out with us if I felt the boys needed it.
Last, if you have to move a meal around or even skip a solids meal, it's not the end of the world. Remember the clock means nothing to babies, and they have no conception of 'set' meal times. The approach I take to solids is to fit it in when it works, but not stress about it if things have to change for a day.
You will quickly figure out what works for your and your LO.