Clothing after weight loss?

So I haven’t lost enough weight to need new clothes yet, but like... how does that work? I wanna lose 100 pounds an obvious with 100 pounds lost I’m gunna go down multiple sizes in pants.

Should I go to Salvation Army/second hand stores to get stuff? I don’t wanna spend hundreds of dollars on pants I’ll wear for 2 months then have to go down another 3 sizes or something 😂

Obviously when I’m goal weight I can buy new. But I’ve never really thought of what people wear between starting weight and goal weight.