Corn, beans, and squash (pumpkin) is a classic traditional polyculture laid out in mounds or hills, one can also plant in swales or on berms depending on the site.  Check ATTRA for a publication on the subject of polycultures or 3 sisters; I have added white clover to the mix for ground cover and nitrogen fixation, which is especially nice for the squash where they send down roots off the vines.  Straw mulch spread about is also nice, and you can even sheet mulch around each mound, but it isn't worth it nor a good idea to fill the field with sheet mulch, rather stick with an uncut straw mulch spread about.  After the squash vines spread they act as mulch and also protect the maturing corn and bean mounds.  Let the Lamb's quarter's grow if it is a weed there and use it in salad.