I understand why someone posted here wondering why BS appeared to be leaving the store empty handed - suspecting he may not have been buying anything but somehow communicating with another individual. But honestly, he could have purchased a small item or two (as some have already suggested ciggies, etc) and have them in his pockets.
Why would knowing the exact items be important or relevant though? General stores would carry many, many small items (none of which would be sinister) that men would keep in any one of their pockets, but I'd think favourite cigs, lighter, gum etc would be most likely in this case.
Stopping at one or even many stores on the way home after being incarcerated doesn't strike me as being very noteworthy or suspicious at all - just someone trying to get back to normal, or yes ... even present the image that they have nothing to hide.