As you might imagine, I've got scads to say about this.
Just go slowly. It wasn't all accumulated in one day, so it won't all go away in one day, either.
If you're committed to dumping out stuff, make it something you do more or less daily (you take a day off? Fine!), but in small chunks.
One day: shirts in the closet. Just shirts.
Day two: just skirts.
Day three: just pants.
Day four: just sweaters.
Day five: just dresses.
Day six: just suits.
Day seven: shelf one.
Day eight: drawer one.
Or whatever floats your boat. If you have a lot of matched pieces, you might want to work on them together, e. g. you'll never wear the periwinkle outfit again, nope, it doesn't work with anything else, not even the separates, okay, off they go.
One thing here, turbotax offers it, is a listing of how much everything is worth for your taxes. I have started to put together stuff and also a list. It's very satisfying to see -- this is going to be $20 off next year, this will be $14, this will be $22 or whatever. You need not be that organized about the actual discardings. This is just something that's working for me, personally. I just like seeing it cumulate and turn into something tangible, a reward for being neater.
As for food, the way to work on this is to (a) do the discarding as you are doing it and (b) make shopping lists. The detailed kind. We have a program (RP does it in Autocad but it can just as easily be done in Word or Excel or even Notepad) with the list in it. Need a list? Print it out. We have a bunch printed out and stuck to the fridge with a clip with a magnet. A pen is attached. See something you need? Check off the box. Don't need it? Cross it out. But this list is detailed and even organized by aisle (if the store changes where things are, change the list). And it's got spaces for extra stuff. But there are staples we buy every week -- milk, bagged salad, that sort of thing, and this list has all of that on it. Do we impulse buy weird stuff? Rarely. There isn't a lot of room on the list for it, or in our budget. Once the staples are bought, we don't do a lot of impulse shopping. And, of course, we only buy on full stomachs and we also make sure to check the fridge and pantry before going to the store.
Also, store the food better, Anything in an opened cardboard box should be transferred to a closed ziplock bag. This is good to keep out insects but not mice. If you need to keep out mice, you need a stronger barrier, such as a canister. We have several nice ones on counters, but also plastic ones (rice and cous cous are sold that way here, so we just pull off the labels and wash out the containers. Instant less than attractive but very functional canister) that are kept inside the cabinets. You can also organize stuff by keeping it in lines, e. g. all of your canned tomatoes are next to the left-side wall of a cabinet, all your canned soup is next to the right side wall or whatever. That way you know what is there and you also know what you're running out of.
You can do it!!