Animal Crossing: New Horizons - All 40 slots
Item ID list (thanks Imthe666st)
Make sure there is nothing in your inventory before use. If anything is in any slots, it will be gone or overwritten by whatever item you put in the code. Back up your save, I did not test these and I'm not positive how accurate they are. I'm just guessing based off of patjenova's work.
04100000 AC3B90C0 0000xxxx <--- for the item itself, make sure to put a 0 in front if there are only three characters, like 0aaa.
04100000 AC3B90C4 000000xx <--- for the stack amount, some materials can stack up to 50, 30, 10, etc. 00 = 1 item, 09 = 10 items, 1d = 30 items. You can use this to get the stack number you want, just make sure to subtract by one. If you want 30 items for example, then enter 29 into the decimal to hexadecimal converter. Note: only certain things can stack like material. Most material stacks up to 30 but some stacks up to 10 only such as cherry-blossom petals, fruit, bamboo spouts, star fragments, etc.
[Example code - 10 stack of maple leaf]
04100000 AC3B90C0 00001cce
04100000 AC3B90C4 00000009
[Example code - 30 stack of bamboo piece]
04100000 AC3B90C0 000009c5
04100000 AC3B90C4 0000001d
--- paste below, again, this is untested and I have no idea how accurate it is. back up your save
[1]
04100000 AC3B90C0 0000xxxx
04100000 AC3B90C4 000000xx
[2]
04100000 AC3B90C8 0000xxxx
04100000 AC3B90CC 000000xx
[3]
04100000 AC3B90D0 0000xxxx
04100000 AC3B90D4 000000xx
[4]
04100000 AC3B90D8 0000xxxx
04100000 AC3B90DC 000000xx
[5]
04100000 AC3B90E0 0000xxxx
04100000 AC3B90E4 000000xx
[6]
04100000 AC3B90E8 0000xxxx
04100000 AC3B90EC 000000xx
[7]
04100000 AC3B90F0 0000xxxx
04100000 AC3B90F4 000000xx
[8]
04100000 AC3B90F8 0000xxxx
04100000 AC3B90FC 000000xx
[9]
04100000 AC3B9100 0000xxxx
04100000 AC3B9104 000000xx
[10]
04100000 AC3B9108 0000xxxx
04100000 AC3B910C 000000xx
[11]
04100000 AC3B9110 0000xxxx
04100000 AC3B9114 000000xx
[12]
04100000 AC3B9118 0000xxxx
04100000 AC3B911C 000000xx
[13]
04100000 AC3B9120 0000xxxx
04100000 AC3B9124 000000xx
[14]
04100000 AC3B9128 0000xxxx
04100000 AC3B912C 000000xx
[15]
04100000 AC3B9130 0000xxxx
04100000 AC3B9134 000000xx
[16]
04100000 AC3B9138 0000xxxx
04100000 AC3B913C 000000xx
[17]
04100000 AC3B9140 0000xxxx
04100000 AC3B9144 000000xx
[18]
04100000 AC3B9148 0000xxxx
04100000 AC3B914C 000000xx
[19]
04100000 AC3B9150 0000xxxx
04100000 AC3B9154 000000xx
[20]
04100000 AC3B9158 0000xxxx
04100000 AC3B915C 000000xx
[21]
04100000 AC3B9008 0000xxxx
04100000 AC3B900C 000000xx
[22]
04100000 AC3B9010 0000xxxx
04100000 AC3B9014 000000xx
[23]
04100000 AC3B9018 0000xxxx
04100000 AC3B901C 000000xx
[24]
04100000 AC3B9020 0000xxxx
04100000 AC3B9024 000000xx
[25]
04100000 AC3B9028 0000xxxx
04100000 AC3B902C 000000xx
[26]
04100000 AC3B9030 0000xxxx
04100000 AC3B9034 000000xx
[27]
04100000 AC3B9038 0000xxxx
04100000 AC3B903C 000000xx
[28]
04100000 AC3B9040 0000xxxx
04100000 AC3B9044 000000xx
[29]
04100000 AC3B9048 0000xxxx
04100000 AC3B904C 000000xx
[30]
04100000 AC3B9050 0000xxxx
04100000 AC3B9054 000000xx
[31]
04100000 AC3B9058 0000xxxx
04100000 AC3B905C 000000xx
[32]
04100000 AC3B9060 0000xxxx
04100000 AC3B9064 000000xx
[33]
04100000 AC3B9068 0000xxxx
04100000 AC3B906C 000000xx
[34]
04100000 AC3B9070 0000xxxx
04100000 AC3B9074 000000xx
[35]
04100000 AC3B9078 0000xxxx
04100000 AC3B907C 000000xx
[36]
04100000 AC3B9080 0000xxxx
04100000 AC3B9084 000000xx
[37]
04100000 AC3B9088 0000xxxx
04100000 AC3B908C 000000xx
[38]
04100000 AC3B9090 0000xxxx
04100000 AC3B9094 000000xx
[39]
04100000 AC3B9098 0000xxxx
04100000 AC3B909C 000000xx
[40]
04100000 AC3B90A0 0000xxxx
04100000 AC3B90A4 000000xx