If they're nursing, some sort of nursing pillow was a lifesaver for me. (I had a boppy, other people have raved about other brands and boppy allegedly doesn't fit some larger women well)--and my husband used it a lot too when holding/feeding the babe.
I've also called down a blessing on the people who got me extra covers. I still use the boppy w/ my 2 YO, but we don't have emergency cover-needs anymore.
(and in the 'emergency cover' needs, extra sheets--plain, cheap white ones that don't have to 'match' anything...those are a godsend at 2 am.
And these are hard to find but may be one of my favorite products of all time--I put them in cribs, I put them on changing tables, I tuck them in diaper bags for an on the go pad...heck, I've used them under the dog
They're a 'soft' flannel covered waterproof mat--washable. They're not as 'pretty' as some of the other products like this but they work better, IMO.
For cloth diaper people, some 'good' prefolds (generally not the ones like gerber you can buy in average stores) are worthwhile and, if you're crafty, are easy to 'embellish
'--and actually, non-cloth-diaper people use 'em as burp cloths (and it's nice to have pretty ones now and again
. Green Mountain is good, as is Little Lion (although LL was headed out of business last I checked).
Cloth diaper is hard to answer for because there are SO many options--what I might recommend depends on what system she's using, but I will say a lot of Cloth Diaper people need wetbags and neglect to realize how important extras of those are (ask me how I know
. Actually, don't
). Personally, I REALLY like my rump-a-rooz wet-bag/pail liner the best of the brands I've tried. (and even if one doesn't cloth diaper, a small, diaper-bag sized wet-bag is nice for the diaper bag, IMO. Because every once in a while, parents have to transport something icky)
And most CDers who are doing something other than pocket-diapers or all-in-ones could use a handful more re-usable diaper liners (like these