Maybe get in some nak’d bars or Eat Natural bars to nibble, also nuts and maybe something like ready made smoothies - I know none of these are as good as making your own, but they aren’t bad as substitutes until you have some more time. Also, when you feed your 3 year old, sit down and eat what they have - it might not be exciting or hugely nourishing, but at least it is something.
Gah, in my first 9 months or so of breastfeeding I am so hungry that I have to eat, and eat, and eat. Whole packs of biscuits, plate of homecooked stuff, then same again as seconds, then pudding, then half an hour later, I have more pud. Strangely, I put weight on, but I am sooooo hungry that I just can’t stop. I mean I am ravenous, like walk a mountain for a few hours hungry - but several times a day. How strange and wonderful are our bodies.