You'll probably find yourself much more confident when the twins come and experimenting more with that newborn hold
16 days old and I'm still catching most poos in the chamber pot, laundry sink and a couple of times over the loo when out and about. I remember DD1 getting agitated before a wee would come and this one gets frantic just before her wee comes out! Pretty unmistakeable when she needs to 'let go'. The poo doesn't have as much in the way of signs, but generally comes with every few wees.
I've bought a few MCN's for outings and I can whisper the cues in her ear if I can't get away to hold her over a loo or garden bed.
I was out in the garden with DD1 and 2 the other day and I hadn't brought any extra nappies with me when I realised DD2's nappy was a teeny bit damp. I held her out over the grass for her poo and wee and was able to put her back in the mostly dry nappy and keep doing that until we went back inside to my nappy stash - no panic, just a 'oh, yeah, we don't NEED those' and then used leaves to scrape off any traces of poo!
It's a fun journey.