Good socks and underwear are highly recommend. Issued dress socks and underwear are not good. Below are what DS took to beast last year and had no issues with blisters or chafing.
Dress socks for low quarters-black cushion type sock rather than thin dress sock.
Hanes Men's ComfortBlend Max Cushion Crew Socks 6-Pack, Black Shoe Size: 6-12
https://www.amazon.com/dp/B01FRBTPHK/ref=cm_sw_r_cp_tai_-T9tEbT7PD1B8
Boot socks
Fox River Men's Wick Dry Maximum Mid Calf Military Sock, 3 Pack (Black, Large)
https://www.amazon.com/dp/B06XP75BYN/ref=cm_sw_r_cp_tai_W79tEb2CBT2XE
Underwear-No logo dri-fit type (nocotton) boxer brief with 6” inseam to not show past PT shorts. Very hard to find without some type of logo on the waistband. DS found some all black ones at Target with barely visibly logo and he said they were fine. As last resort, logos can be blacked out with laundry proof marker.