I will save 1 pair of fat jeans so that I can put them on after I hit my goal and the rest I will get out of my house! Not a good thing to keep around.
I did run into a problem the other day - I needed to do a messy home improvement job and I did not have a pair of jeans that fit that I could sacrifice because they are all new.
If you are buying clothes at a rapid rate, I would save a pair of 2 sizes too big jeans to wear for gross work (cleaning, painting, yard work, etc).
I ended up asking my husband for a pair of his pajama pants that I know he doesn't like - they are flannel and comfy. And I was very stoked to be wearing a men's Medium on my newly size 14 tush!
(and my NSV - I just threw away ALL my underwear and bought 3 packs of Hanes size 7!)
I have given most of my grown out of clothes to the Goodwill. However, I had 4 pairs of pants that I neglected to try on during my losses and alas, they now do not fit. Two of them have never been worn, just tried on - so I gave those to a co-worker. I have two more pairs that I'd like to see if they can be altered to fit me... but I have a feeling that 4 sizes down might be too many for dress pants (since I wouldn't have them tailored until I lose all my weight).