Sack packs are a simple bag you can carry quite a load in. I think a Kiwi name for them might be pikau
The simplest is just a feed sack or fertiliser bag with rope 'straps' tied to the bottom corners. You need something like a small pebble in each corner to stop the rope slipping off. It has been suggested that you can have onions or potatoes in the corners of the bag so you have some food with you.
The rope on a sack pack can be one continuous length with each end tied to a bottom corner, and a cow hitch is made at the mid-point of the rope which is then hitched over the bunched neck of the sack to hold it shut and provide the top anchor point for the rope(s) which then becomes a set of shoulder straps.
A sailmaker buddy made a wonderful light canvas sack pack for me. Instead of having rope for the shoulder straps it has nylon webbing, but the webbing is fastened at either end with cord..... the bottom cords being adjustable. Instead of having a stone in each corner, the fastening 'anchors' are sewn into reinforced patches in the corners of the bag.
I also have one that I made from polarfleece fabric. This fabric appears to be relatively tough and strong... and it is quieter than canvas when it brushes against things in the bush. This, too, has webbing straps. Like the green pack, there is a strip of webbing sewn along the bottom for reinforcing, and the cord anchors are doubled-over strips of webbing sewn in at the bottom corners.
Although my sack packs appear to be small, they are still useful. I managed to pack all the boned-out meat from a young red deer stag into the green pack. It was very heavy I might add.
I think it is best if the straps on the pack are joined together at the top as it makes it easier to tie the top securely. Here is a knot that I have found to be very reliable for tying the top of the bag (I would describe this as a slipped reef knot with an extra pass in the second stage). The diagram, for simplicity, shows only one pass of cord around the neck of the sack. It is more secure to pass the cords around the neck twice before tying the knot:
A sack pack may not look as good to some folks as the day packs in a glossy catalogue. It does take a while to open and close it. But it has smooth lines and can be toted through the scrub with much less chance of getting hooked up than a framed pack or one with lots of straps and protrusions. If the bag material is waterproof, then your load should stay fairly dry. If you are hunting and only need the bag to carry your jacket when you get too hot and maybe carry the meat home, then you can stuff the empty pack down your shirt to keep it out of the way when stalking. Above all it is relatively inexpensive and you can make it yourself.