Wherever you go, there you are.
Dumb Little Man talks about meditation without meditating.
If you’re queueing at the post office then why let yourself get upset and frustrated? Why not just accept that you’re there and practice mindfulness instead. Bring your full attention to your surroundings; the people, the sights, the sounds. Involve all of your senses. Be aware of any inner dialogue that may be judging, criticizing, wanting, resisting. Breathe in and out and allow yourself to be completely calm. Don’t drift off in your thoughts. Be wherever you are, fully.