Solution by Garry FRANCIS

This is a minimal solution. You'll need to EXAMINE lots of things for this solution to make sense. Some optional (but significant) commands are shown in parentheses. These can be omitted once you know what to do.

001 - (X ME) (you're naked)
002 - S
003 - E
004 - E
005 - GET BRANCH
006 - (X IT) (it would make a good club)
007 - W
008 - S
009 - (X PLANT) (it's covered in gelatinous fruits)
010 - GET FRUIT
011 - (X IT) (transparent skin covering slimy substance & has sweet scent)
012 - N
013 - N
014 - N
015 - E
016 - N
017 - (X TORTOISE) (it's covered in ants)
018 - (X ANTS) (there are thousands of them)
019 - (GET TORTOISE) (keep your distance from the ants)
020 - DROP FRUIT (ants tear fruit into pieces and carry them away to their nest)
021 - GET SHELL
022 - (X IT) (top half would make good container if you could remove bottom half)
023 - U
024 - U
025 - S
026 - THROW SHELL INTO CHASM (you hear hollow clunk when it hits bottom)
027 - N
028 - D
029 - D
030 - S
031 - W
032 - W
033 - U (or CLIMB TREE) (note that height of tree makes it vulnerable to lightning)
034 - HIT SNAKE WITH BRANCH (it's now bloodied and lifeless)
035 - GET IT
036 - (X BRANCHES) (note that branches have been struck by lightning in the past)
037 - D
038 - S
039 - E
040 - E
041 - N
042 - E
043 - N
044 - D (there's a sabre-toothed tiger here)
045 - DROP SNAKE (tiger drags it off to the north to eat at its leisure)
046 - E
047 - X RUBBLE (you find a sharp-edged piece of obsidian)
048 - GET OBSIDIAN
049 - W
050 - N
051 - GET SHELL
052 - (X IT) (it's the top half, the bottom half is broken off and lost in the rocks)
053 - S
054 - (S)
055 - (X WALL) (there's a narrow slit blocked with debris, so come back later)
056 - (N)
057 - U
058 - S
059 - W
060 - S
061 - W
062 - S
063 - FILL SHELL WITH WATER
064 - GET FRUIT
065 - N
066 - E
067 - N
068 - E
069 - U (the grooves contain some molten metal)
070 - POUR WATER ON METAL (shortly after this, the sky darkens as a storm approaches)
071 - GET METAL
072 - D
073 - W
074 - S
075 - W
076 - N
077 - W
078 - U (or CLIMB TREE)
079 - PUT METAL IN NEST
080 - D (wait until lightning strikes, if it hasn't done so already)
081 - (X TREE) (you wonder if you can make use of the fire)
082 - (X FERNS) (the smoke and smell would scare off any predator)
083 - LIGHT BRANCH (or BURN BRANCH)
084 - S
085 - CUT FERNS WITH OBSIDIAN
086 - GET FERNS
087 - E
088 - E
089 - N
090 - E
091 - N
092 - D
093 - S
094 - (EXAMINE WALL) (there's a narrow slit in the wall)
095 - (S) (you're carrying too much to squeeze through the crack)
096 - DROP ALL EXCEPT FRUIT
097 - (S) (you still can't squeeze through, perhaps if you were more slippery...)
098 - SPREAD FRUIT ON ME
099 - (X ME) (you're now covered in a gelatinous substance that makes you slippery)
100 - (S) (you can now slip through)
101 - (N)
102 - GET BRANCH
103 - S
104 - DROP BRANCH
105 - N
106 - GET FERNS
107 - S
108 - DROP FERNS
109 - N
110 - GET OBSIDIAN
111 - S
112 - GET ALL (ferns and branch taken)
113 - E (there's a woman stuck behind brambles being terrorised by a dinosaur)
114 - (X WOMAN) (she's screaming a lot)
115 - DROP FERNS
116 - BURN THEM WITH BRANCH (the smoke drives the dinosaur away)
117 - CUT BRAMBLES WITH OBSIDIAN (woman escapes brambles, she'll now follow you)
118 - DROP OBSIDIAN
119 - W
120 - N
121 - N
122 - N
123 - N (tiger scared off by fire and you both live happily ever after...hopefully)