Mine are 3yo and 8mo, I'm still on mat leave, and I feel exactly the same! It's relentless. Things which help are:
Keeping the freezer stocked with meals that we can take out for dinners. We'll cook big batches of food eg bolognese, and freeze enough for a couple of meals. That way I don't have to cook from scratch every day.
Meal planning in general. Between dp and I we generally know what we're having for dinner for the next few days. We freeze meat and fish and take out what we need to make dinner in the morning.
If possible, preparing dinner in the morning, as completely as possible. The baby is usually asleep for his longest nap, and neither kid is tired or cranky.
Everybody eating the same thing, so I'm not doing separate meals for me/the baby/dd. One lunchtime after ds went onto solids I realised I was doing three different lunches- bloody ridiculous!
Making lunchtime a spread of finger food- pitta, hummus, crudite, avocado slices, ham, cheese etc. minimal prep and the baby can feed himself. Blimey, a lot of these are about food!
Dd (3) goes to playgroup two mornings a week, and that has been a sanity saver. It's free.
Although dd doesn't nap any more, we have quiet time after lunch. Hopefully ds is napping at this time, though that doesn't always happen. She watches a tv prog, listens to a story cd, or looks at books. The understanding is that I sit down and have a cup of tea and it is MY quiet time too. She is pretty good about it.
It really helps to prepare for the next trip out, as soon as we get in from the last one- ie sort out changing bag etc. The theory is that we can then just leave the house easily. I hardly ever actually do this though!