There are some good local markets off-post :)

E-mart (20 mins from Camp Humphreys)
https://www.google.co.kr/maps/place/%EC%9D%B4%EB%A7%88%ED%8A%B8+%ED%8F%89%ED%83%9D%EC%A0%90/@37.0168273,127.0729881,15.65z/data=!4m17!1m11!4m10!1m3!2m2!1d127.0759205!2d37.0241483!1m5!1m1!1s0x357b3bb630760959:0x5fd9e304b5f19e83!2m2!1d127.0755794!2d37.0210166!3m4!1s0x357b3bb630760959:0x5fd9e304b5f19e83!8m2!3d37.0210166!4d127.0755794

Lotte Mart (15mins from Camp Humphreys)
https://www.google.co.kr/search?q=korea+mart&oq=korea+mart&aqs=chrome..69i57j0l5.8696j0j9&sourceid=chrome&ie=UTF-8#newwindow=1&tbm=lcl&q=pyeongtaek+lotte+mart&rlfi=hd:;si:6689033269889482288;mv:!1m3!1d331.4501175708364!2d127.111806!3d36.9883021!2m3!1f0!2f0!3f0!3m2!1i1116!2i639!4f13.1

Korea mart (5 mins from Camp Humphreys)
https://www.google.co.kr/search?q=korea+mart&oq=korea+mart&aqs=chrome..69i57j0l5.8696j0j9&sourceid=chrome&ie=UTF-8#newwindow=1&tbm=lcl&q=%EA%B2%BD%EA%B8%B0+%ED%8F%89%ED%83%9D%EC%8B%9C+%ED%8C%BD%EC%84%B1%EC%9D%8D+%EC%95%88%EC%A0%95%EB%A1%9C+112&rlfi=hd:;si:18435537091855057152;mv:!1m3!1d5595.511232997552!2d127.05631525001525!3d36.96332135886656!3m2!1i1116!2i674!4f13.1

NH Mart (10mins from Camp Humphreys)
https://www.google.co.kr/search?q=korea+mart&oq=korea+mart&aqs=chrome..69i57j0l5.8696j0j9&sourceid=chrome&ie=UTF-8#newwindow=1&tbm=lcl&q=%ED%8C%BD%EC%84%B1+%EB%86%8D%ED%98%91&rlfi=hd:;si:5452556321552235602;mv:!1m3!1d10925.817184941898!2d127.0423143!3d36.9601345!2m3!1f0!2f0!3f0!3m2!1i747!2i329!4f13.1