It's hard, isn't it... you want to keep them amused whilst you put laundry away, sort dinner, have 5 minutes peace and tidy the house. It's nice to have it done before your DH gets home, so then both of you can focus on dinner, bath and bedtime, before realxing after they go to bed!
We have most of DD's toys in small to medium plastic boxes that you buy from Big W, Target or a cheap store) that have the activities in them. That way you can just get one thing out for her to play with, and it's is fairly easily tidied up, rather than a whole room to tidy.
We have small boxes... a
playdoh one, a
paint one, a
Barbies/ dolls one, a
Little People one, a
baby doll one, a
drawing/ activity book one, a
music one etc. They contain everything she needs, ie. to draw, without any stuff in there that needs supervision.
We also have larger one with the
Little People house etc., one with
blocks, and one with miscellaneous toys. We also have a couple of larger ones with her
old 'baby toys' in them, which make for great amusement, as we don't get them out very often, so they are very exciting to her!
We also have a
dress up's bag. That stuff often gets dragged out and makes a mess, but very easy to shove it all back in once playtime is over.
She also she has a couple of
baby dolls, and baby stuff for them. Likes to take them in the pram to pretend places,a nd feeds them/ changes them etc. When she asks to play too, it might be a matter of helping her change them, then she goes off by herself again for a while.
DD is really into
books again, but in a phase where she won't sit and look at them by herself, because 'I am too little to read.' But maybe some simpler kids books with lots of pictures, or noise making ones might help?
Another possible thing to amuse them is games on the computer, but most of those require your help anyways. Some sites (Sesame Street, Wiggles, Disney etc.) have story telling and games where the toddler just has to press a button to play...
So, these are not really non-mess making games, but mess minimising ideas... I am not sure no-mess is possible!!

Even when watching TV/ DVD's, DD still manages to make some sort of mess, pulling the cushions off the lounge, playing other games at the same time, wanting food/ drinks, and making a mess with that!! I think the best solution is a nice glass of wine for mummy and daddy after the kids have gone to bed!

Oh, and yes,
the slow cooker is a great way to cook, esp. now the weather is perfect for casseroles, curries and stews. You prepare the meal earlier in the day, when you tend to have more time/ patience! Then in the evening, you can feed your kids their meal from it and leave it on simmer/ warm, so either of you can eat at whatever time you like (can manage it) too.