I have a friend who is just coming off of a 10 day fast. I do 5 or 6 day fasts several times a year as well. One could easily just lay around and not do much and be just fine.
So, so long as there is a water source, mostly the biggest challenge, once one sets up camp, will be boredom.
It's been years, however, I have done 5 days, with just the following.
1. Two 55 gallon drum liners, 2 thermal blankets, and a $4 painters plastic drop cloth (thickest Mil size they had) - The drum liners and thermal blankets were stuffed in my Back BDU Pockets. The painters drop cloth in one of the cargo pockets.
2. I was wearing wool socks, BDUs, a Tshirt a sweat shirt and a pull over style hoodie from Old navy (had not acquired my favorite fur lined one at that time yet)
3. USAF survival knife, and my Gerber gatormate folder. - on belt
4. 5qt Vietnam era collapsible canteen. on sling - on my back
5. Stirkeforce Firestarter kit and a mag block (Had not discovered plain ferro rods and magnesium rods yet) - left front pocket
6. I don't remember what I had for cordage. it was before I started using mason line, so I probably had laundry line, and that stuff that comes with commercial tents that is used as the tieout line. - In BDU cargo pocket
7. My goal was to fast, and not eat in the first place, so I didn't bring food, and did not eat at all. That trip was before I discovered edible plants too.
8. Hygiene was just a 1/4 roll of TP with the cardboard roll removed so I could flatten it out and stuff it in cargo pocket.
9. Map and compass. Map was in BDU pocket with the drop cloth, compass was around my neck
The trip went like this
It was a total guerrilla camping trip.
Girlfriend dropped me off in the woods. She then went to the airport and flew to Omaha to see her family for a week.
I spent the bulk of the first day wandering around looking for the most stealthy place to camp, close to the stream I knew of in the area.
Then I made camp, and a small fire.
The rest of the trip I basically alternated between doing various intensities of Kung Fu till I passed out, laying around, going for water and tending to my fire (which was little more than coals most of the time)....on the last day I packed up and went to the parking lot and hoped she came back for me....
Laying around like a lazy ass was my primary activity.
The camp was just an "A" frame tarp set up on a ridge line between two taller pine trees. The bedding was bunches of pine needles. I slept on top of pine needles, with the the folded over part of the tarp on them. Never even used the drum liners or the thermal blankets.
Two big things I learned that trip.
1. Never set up between two pine trees. They drip sap all over and everything gets sticky.
2. Never collect pine needles for bedding with your hoodie. The left over needles poke you through the fabric when you later put it on at night because the temp drops.
Oh, and also, it always rains at exactly 3:30 AM, but is bright and sunny by sun up, so everything is damp, but it really does not look like it rained unless you were up to see it. You have to protect your coals, by putting all your largest wood on top of them, stuffed together really tight. Then when you flair it up in the morning using debris you collect, it smokes like crazy till the dampness dries out and the coals can ignite them.
So yeah, 5 days with just what is in your pockets is easy. Every survivalist should be able to do this with little effort.