It depends on whether re-supply is actually impossible, or merely slow and expensive.
Most developing countries have markets or shops in which basic cheaper and lower technology goods can be purchased.

Water purification tablets, a bulk supply of 5,000 tablets should last several years.
Several flashlights and a few dozen lithium AA batteries.
Several multi tools or Swiss army knives.
Fire making kit
First aid kit.
That would be the basics for almost any situation, but a lot more MIGHT be needed.

A lot depends on the local availability of basic clothing etc.
Do you need to take a 3 year supply of underwear, shirts, socks and outer clothing ?
A dozen or more pairs of underwear, socks and t shirts can be worn out in 3 years, taking that many would use up a fair bit of the 75 pound allowance. Or can these be obtained locally ?
Unless the area is extremely remote, there will be local people, probably wearing clothes, from where are these obtained ?

Do the local people wear shoes ? if not, you can probably manage without, the pair that you are wearing on arrival should last 3 years of limited use. But if shoes or boots are needed for cold or rough terrain, then several spares pairs will be needed, again do you have to take these or can they be purchased locally.

What is the climate like ? long underwear, heavy clothes, and thick overcoats needed ? plus replacements for 3 years wear.

Staying in a building with cooking facilities and electric lights ? or camping ? Do you need to take enough matches for 3 years ? or just enough for any short term emergency.

Will you need a sleeping bag or blankets, and if so can these be purchased locally or must you take them with you ? You may need replacements, I would not count on even good quality blankets or a sleeping bag surviving 3 years of rough use.

Is a firearm needed for defence against human enemies, or dangerous wildlife. Is a permit or licence needed ? Ammunition for 3 years ?

To summarise, are we talking about 3 years of total self sufficiency, or about staying for the same time in a basic settlement where shoes, clothes, blankets and the like can be purchased.