Mildez - abdominals will always be weaker after pregnancy - but in the case of a severe separation (sign being that the gap inbetween the ab's is greater than 2.5 fingers) then yep, you should avoid doing things like the traditional ab crunch - that'll just cause them to separate more. Push ups are fine as you're facing the ground and need to hold your ab's firm to protect your back from injury, I'd recommend keeping your knees on the ground when you do the push ups though - just until your ab's get a bit stronger.
If you type fatchicslim (no spaces, just as I've typed) into you tube (hopefully its working for you now) there is a video about planks - which is the best way to flatten ab's and help bring those ab's back together. As a general rule I always keep my belly braced throughout the day, sitting, walking, lifting - pretty much with everything I do (ok, maybe not when I sleep lol).
As for bread alternatives, sometimes I have open faced sandwiches (depends what the content of the sandwich is) or another way I like to change it up is with vita wheat type crackers or wholemeal wraps. For some reason any sandwich is 'tarted' up when its in a wrap haha!

