The Monk class in BG2 is hardcoded to have certain items equipped as its fist item at certain levels, to give the THAC0 and damage bonus due to the class. The item for each level can be set by editing the bgmain.exe file (starting at 0x00757FEC in version 2.5.26461). The default item/level mapping is below:

Level	Item File
1-4	MFIST1
5-7	MFIST2
6-8	MFIST3
9-11	MFIST4
12-14	MFIST5
15-17	MFIST6
18-24	MFIST7
25+	MFIST8