D&D 5e Island survival campaign

[PandaPhobia]

I want to run a campaign starting off in a prison in the middle of a boiling lake (a la avatar) and trying to escape the prison. Ideally, they would escape from the prison, find a way across the boiling lake that surrounds it, disappear into the jungle surrounding the lake, make it through the dry forest of undead plants and animals, across some mountains and deserts, dodging the enslaved dragon turtles that guard the island. However, I'm not sure how to spiff up the rules for 5e regarding survival and prevent gaming of the system (e.g. goodberry,etc) and need some help regarding the encumbrance rules.

for encumbrance, I was thinking of just having a maximum amount of "weight points" that every character has, that they can then subtract weight from whenever they need to carry something. (ex. tom has a "weight point" value of 150 pounds, and decides to carry a chunk of rock weighing 50 pounds. he now has 100 "weight points" left. I think it might work, but I need some fresh eyes on it to hopefully come up with something better.

[th3g0dc0mp13x]

1. Modify goodberry so it requires a consumable component. i.e. Mistletoe worth 2 silver.
2. Just use the variant encumbrance rules from the PHB pg176.
-2.1 don't handwave how they are holding stuff. Backpacks only hold so much and it has a physical space.
3. Use some of the variant rules such as equipment sizes, and Healer's kit dependency.

[NinaWu]

Used properly, the encumbrance rules work really well. Especially for those using STR as a dump stat (which seems to be happening more and more). Also, as mentioned, the backpack only holds like 30lbs of gear (if they are lucky enough to obtain one) so it can really force some difficult choices on the PC's.

[Man_Over_Game]

One thing I worked on was a list of possible encounters that utilized Exhaustion/Rations as a resource.

To go a day without exhaustion, you require at least one ration.

To restore hit die during a short rest, you need to consume at least one ration.

To remove exhaustion when you sleep, you need to eat at least two additional rations throughout the day (for a total of 3).

Goodberries count as a single ration.

Events may occur throughout the day that will impact their ability to gain food, improve sleeping conditions or expend energy.

An example I like to use is a simple mirage encounter:
The players see what appears to be an oasis. Roll a 1d4 in secret. If it's a 1, the oasis is real, otherwise it's a mirage.
A successful Investigation/Perception check of 20 will indicate whether it's real or not. Any players who see through the mirage get inspiration. If none of the players see through the mirage but they decided to investigate, they each spend an additional ration this day recuperating from the additional distance lost.
If the oasis was real, and the players rested within it, they sleep in comfortable conditions, gaining 3 rations each.

These circumstances should only last for as long as the players are outside and in the wilderness. The lack of comfortable sleeping conditions and harsh climates mean they have to spend more food/time to be well rested.