Clothes - a good problem!

Learn some basic tailoring maybe? I've had to take in (and let out) a few dresses in the past, if you stick to the original seams and only take stuff in a small amount (half inch or so) it's easy and no one's ever noticed.
or a clothes swap? see if they have one nearby or you could organise one.

I had bought some basic items in stretchy materials to help get me through. I can still wear my size 8 pants because I bought them all in skinny leg and I just wear a belt and deal with the fact that my butt area is a little saggy lol.

Also, some dresses in similar types of fabric that don't look so bad bigger. I would hit up stores like Old Navy for some of these items at a good discount - especially now when they're having big sales.

Find someone in need and help them out. Doing a good deed like that will make you feel at least a little better about having spent the money because it isn't "wasted". Hopefully whoever needs those sizes could also be inspired to get in better shape and pass them along when they are finished with them.

You could also keep a few of the clothes in each size as you go. When you are done losing take all of those clothes and make a quilt out of them. I know i am crazy but i see unwearable clothing as fabric. Materials like that are quite expensive these days, so they would make an awesome memory quilt. Many milestones could go into one throw.

As for new clothing. Just buy what you need as you need it. Get just enough to get you through and if it is not enough then it could inspire more weight loss maybe.

I don't have to worry much about fashion so i just keep tightening my belt and i wear a lot of sweatshirts and tshirts. I think i have clothes with tags on still in my closet so i need to go shopping at home lol

Stretchy fabrics, sales and second hand shops are how I'm dealing with it.

Ok, I'm actually mostly dealing with it by wearing my too-big-baggy-bummed clothes* round the house, and saving two or three outfits (bought second hand or in the sales) that fit for going outside. Because I'm greedy, and I'd rather spend the money on lovely lovely food than on something that might only last a few months. :-)

* I did actually invest in a new belt to stop them falling down. From Ebay. I'm not that much of a skinflint.

I try to stick with basics that can be layered. A plain black t-shirt that you wear today may still be wearable under a sweater or jacket next fall. It depends on how much you lose, of course, but there is some give.

It does add up though. A year ago I as 16w/18regular and now I am size 10/medium. My standard when I get to a new size is to buy a pair of black pants and, if the size I just left really looks bad, one other pair of pants. Air dry everything until it starts to get loose. Then stick it in the dryer to shrink it up a bit. Eventually you have to buy the next size or else you will look messy. Dresses are nice because there's a bit more leeway with them if they have full skirts.

My sister looks on the Facebook yard sale sites in our area and finds TONS of clothes for cheap. Also Craigslist. People are trying to get rid of clothes they don't fit in anymore.

Thrift stores.
Second hand and consignment stores.
Find a good and affordable tailor.
Yard/garage sales.
eBay
Facebook (look for local sale/swap/barter/buy pages)
Craigslist

ETA: You can sell your old stuff to get some money back that can towards replacing what you sell. You can sell at Thrift stores (sometimes), second hand and consignment stores, yard/garage sales, eBay, Facebook, and Craigslist.

I'm always up for shopping! (Of course I get that its expensive, so I'd go with stretchy stuff maybe?)

I only bought bottoms when mine were falling off (yes even panties), and only a couple (and tight). Didn't buy any shirts at all until I was 10 pounds from my goal weight because I figured I'd still wear them at goal weight... Nope, they were too baggy, and I actually gave them all away a couple weeks ago and wish I had saved the money... same with the jeans I bought 8 pounds ago (although to be fair, I pretty much had to buy jeans at that time anyway, I guess I lost more sizes than I thought I would, and I'm still not at my goal weight yet).

So my advice is to save your money until you're at your goal weight, and in the meantime just replace things that fall off (for me it was pretty much at season change). I'm cheap though, and basically only buy basics on sale and/or with a coupon (Old Navy, Kohls or Target pretty much).

I've been buying 2-3 dresses at a time as I drop down in weight. One size up doesn't look atrocious with a belt and cardigan. A few cardigans + 3 dresses that fit and 3-6 that are only a little too big = enough variety to get by. As clothing becomes unwearably large, I donate it.

I buy my dresses at Ross/TJ Maxx for $15-30 and cardigans at Target for $3-5.

I'm about to exit from a lot of sizes all at once (I was size 10-12 for a long time before I dropped down to 6-8), so I may try going to Plato's Closet, which is a store that buys gently used on-trend clothing and accessories. You can get cash or store credit, though I've heard it's like, "I will give you $2 for this dress or $3 store credit."

I'm a Gywnnie Bee member and love it. I figured there was no point in buying more clothes until I get closer to my goal so I just pick what I like, wear it a couple times, and send it back. That way I can keep adjusting the size as I lose.