I had the pleasure of doing both to my ex-wife. I tried a couple different mummifications. The first few were done with a large bed sheet and separate sections of rope wrapped outside the blanket. I also tried looping one large length of rope in a series of half hitches from ankles to chest. That seemed to work best. I of course left her head and feet out of the wrap. The blanket offered some freedom of movement, more than I cared for. She could roll around and actually sit up. Her feet were almost completely helpless. Since I didnt tie her hands together before i mummified her she was able to move her arms around and eventually work her way free. This was not the case when I did the plastic food wrap mummification. The plastic wrap offered less freedom of movement than the sheet did. We found that escape was not possible, and she did try. The major disadvantage is that the plastic is very very hot, hence it's uncomfortable and I would say dangerous. The mummifications were fun and made for some nice polaroids but I didn't care for them as part of my normal scene.
The sand burial is a different story. A friend told us about this place called Assateague Island. It's a national park that is part of Delaware and Virginia. There are limited access beaches, about 100 miles worth. You need a permit and a 4x4 to access them, or of course you could walk on them. We went down there and drove onto the beach, about 20 minutes later we were on our own secluded beach, ocean in front, sand dunes behind. The people that were out there with us were looking for the same thing, seclusion so people set up far apart from each other. If you love the beach this is the place for you. If you love buried in the sand tickling, this is also for you!!! She only let me do it once after I pested her for hours.
I dug a hole in a way that when she sat down in it her body was in a sorta V shape. I tied her wrists together and tied them to her waist so she couldn't get her hands out of the sand. I also tied her knees and ankles together, then i covered her up with the sand. I thought she'd be able to lift her legs and move them around, but it turns out that the weight of the sand or maybe just the V position made it tough for her to life her legs at all. This ended up being an escape proof perdicament for her. Her feet were incredibly ticklish for about 10 or 15 minutes before it wore off (that was typical for her). It was a good 15 minutes anyway.
Doubt that this will ever be recreated, my current wife wouldn't go for the outdoor thing.