I think my limit for walking to work or store would be 1.5 to 2 miles. As it is I walk 3-5 miles for exercise every other day and I enjoy it immensely, but I would not want to have to carry packages or bags that far.
Currently my bike is my go-to option for most errands under 30-miles R/T, and I think my absolute limit for biking on an errand would be 40-50 miles R/T. This is based on my suspicion that I would be physically incapable of finishing anything further in a timely (to me) fashion.