1) The first clue says that the backpack and the mini skirt are kept (K).
2) The clue from the backpack says that none of the hats were kept, which means that the blue cap, the black beret and the sombrero are all either thrown away or donated (T)/(D). It also says that either the red scarf or the blue suede shoes are kept. These clues will be useful later.
3) The clue from the mini skirt says that only two of the three blue items (Blue Jeans, Blue Cap, Blue Suede Shoes) are donated (D). We also find out that the brown socks are thrown away (T).
4) The clue from the brown socks says that the flip flops are adjacent to two kept items. We know that the Sombrero can’t be one of these (see #2). Therefore, we conclude that the metal t-shirt and the basketball shorts are kept (K).
5) The clue from the basketball shorts says that row 4 is the only one that has no (T) items. This means that the red scarf and the blue suede shoes are either K/D. We already knew that one of them is kept (see #2); we now conclude that the other is donated.
6) According to the metal t-shirt clue, the (T) items on the fifth column are not adjacent. We can conclude that there must be two of them (if there were three, two of them would be adjacent). Hence, the flip flops are (T) for sure, and either the fleece jacket or the corduroy pants is also (T).
7) The flip flops clue tells us that the swimsuit and the bikini are kept (K).
8) Using the clue from the bikini, we can say that the blue jeans, sneakers, white t-shirt and green sweater are either (T) or (D). Then, we can conclude that the two kept items mentioned in the swimsuit clue can only be the leather jacket and the purple tank top (the black beret was not kept, according to the backpack clue).
9) The leather jacket clue says that the white t-shirt is donated (D), and so is either the red scarf or the red pants.
10) If the white shirt is donated (D), then the blue jeans must be thrown away (T), per the clue from the basketball shorts. In that case, the blue suede shoes and the blue cap are the two donated (D) blue items mentioned in the mini skirt clue.
11) We know that there was one kept (K) item adjacent to both of the strapless items. Since we have found out that the suede shoes are donated, then the kept item must be the red scarf. Which, in turn, means that the red item that was donated (leather jacket clue), is the red pants.
12) The clue from the purple tank top says that three columns have over two kept items. We already know that the sneakers, the beret and the green sweater were not kept. This leaves columns 2,4 and 5 as the ones with more than two kept items. So, the black jeans must be kept (K). This also means that there is one more kept item in the fifth column. One of the two items left on the fifth must be thrown away per the heavy metal t-shirt clue, and if the fleece jacket is not thrown away (red scarf clue), it means that it is the kept item, whereas the corduroy pants are thrown away.
13) The corduroy pants clue says that 13 items were kept. We have 12. Out of the remaining boxes, the strapless dress is the only one that can be the 13th kept item (see #2 and #8).
14) The clue from the dress says that if the green sweater is donated, then the beret is kept. We know that the beret was not kept. Hence, the sweater was not donated; it was thrown away (T).
15) Using the clue from the sweater, we can say that the columns 1,3 and 4 have at least one item of each status. This means that the sombrero was donated (D).
16) Using the sombrero clue, we can conclude the sneakers were thrown away (blue jeans is the other box that is surrounded by kept items).
17) With the last clue, we find out that there were 5 donated items in total, all of which we have discovered. That leaves (T) as the only option for the beret.