[RPG] the weight of a laden adventurer

Make a GMPC that cannot help

Good examples of this are for example golems, zombies, or animal companions. You can ask them for help all you want; they cannot make decisions for themselves and only follow orders. They might instinctively fight on their own accord, protect their charge with their lives and follow him anywhere but no matter how often you try, they won't be able to pick whether you should go rescue the princess immediately or find the magic sword first.

Make a GMPC that is not allowed to help

Perhaps the companion is tasked by a Holy Order to escort the PC, because according to a prophecy the PC will recover an ancient artifact. But the prophecy also says that the PC will travel there on their own accord and their minds cannot be influenced by those who know the contents of the prophecy. So the companion will guard and help the PC with anything they ask, but they cannot influence their decisions directly for fear of ruining the prophecy.

Alternatively, the companion could just have a very strong belief that the PC should be solving this problem on their own. They could be a mentor from a monastic order teaching them about decisions and responsibilities, for example. Or a military leader training an officer to deal with complex situations.

Make a GMPC diametrically opposed to going forward

For example, a bodyguard who is under strict orders to follow the PC wherever they go and never go against their command, but who really just wants the PC to go back home and give up this foolishness. They will never say so, but if you ask, their only advice is "turn around and march home", which is not exactly helpful.

Make a GMPC that cannot communicate with the PC

A mute, for example. It would take quite some adventuring before the PC can learn sign language to the point where the companion can do much more then point at things and do some gestures. This one can give some help, but as long as you as the DM don't talk it's very easy to stay in character and you probably won't be able to give away much. (It's also funny to have to do charades)

So, ultimately, we're looking at a way to maximize a PC's strength score, and multiply their carry capacity as many times as possible. This is easy enough.

You need a Goliath, Orc, Bugbear, or Firbolg (all from Volo's Guide) who is an 18th Level Druid. They should be wearing a Belt of Frost Giant Strength and carrying a pile of Potions of Growth.

Those 4 Races have the following Feature:

Powerful Build: You count as one size larger when determining your carrying capacity and the weight you can push, drag, or lift.

Our 18th Level Druid should shapeshift into a Mammoth. A Mammoth has a Strength of 24, and is Huge. By default, this gives the Mammoth a carry capacity of 1,440 lbs.

Now, because Wild Shape specifies that

You retain the benefit of any features from your class, race, or other source and can use them if your new form is physically capable of doing so.

It seems that Powerful Build still applies while Wild Shaped. So, our Mammoth counts as Gargantuan for determining carry capacity. This takes us up to 2,880 lbs.

Now, the spell Enhance Ability has a Material Component, so the Druid cannot cast this spell while Wild Shaped. But, shapeshifting doesn't break concentration on the spell. So the Druid can cast the spell on themselves as Bull's Strength, then shapeshift, and grab their load. This doubles our carry capacity again, taking us up to 5760 lbs.

Next up is a bit of a conundrum. Normally, I'd suggest using a Potion of Growth to increase your Size Category...but you already count as Gargantuan for determining your carry capacity...and per RAW, there are no sizes in 5E that are larger than this. So we'll skip that one for the moment (don't worry, we'll come back to it).

Because we're dealing with a Mammoth here, and given the sheer volume of cheese we are moving, I'd suggest using a Cart. This lets us use the Mammoth's Pulling capacity, taking it up to 11,520 lbs.

But wait, there's more! Wild Shape also specifies this:

You choose whether your equipment falls to the ground in your space, merges into your new form, or is worn by it. [...] Equipment that merges with the form has no effect until you leave the form.

When you shapeshift...anything you are carrying is basically gone...merged into your form having 'no effect.' This is generally interpreted to mean that they also have no weight while you are shapeshifted.

So...our Druid should pick up as much cheese as possible before they shapeshift.

Our Druid is wearing a Belt of Frost Giant Strength and has cast Enhance Ability on themselves. This gives them a strength of 29, doubled carry capacity, and they count as Large for determining their capacity. So they can carry 1,740 lbs. Chug that Potion of Growth now, and become Size Large, counting at Size Huge...and double your capacity again: 3,480 lbs.

So, our Druid will cast Enhance Ability on themselves, knock back a Potion of Growth if they need it, then pick up 3,480 lbs of Cheese, then immediately Shapeshift into a Mammoth and hook into a Wagon loaded with 11,520 lbs of Cheese. Giving us a total cargo capacity of 15,000 lbs of Cheese.

They'll need to stop once an hour to refresh the spell on themselves, and will need a Short Rest every 2 hours to reset their uses of Wild Shape (get a 20th level Druid if you don't want that break every 2 hours). But they shouldn't have any problem meeting the standard 8 hours per day of travel time.

(Note: If your DM rules that the Colossal size category exists, then the effect of the Potion of Growth on your Mammoth form will apply, doubling your drag capacity yet again).

Addendum: If you don't trust Shapeshifters...and letting them magically absorb your Cheese, then get yourself a Multiclassed Barbarian 6/Sorcerer 5. The Barbarian should be a Totem Warrior, and have taken the Bear Totem feature at 6th level. The Sorcerer should have the Extended Spell Metamagic. Otherwise, keep race and magic item collection the same. This caps you at 13,920 lbs pulled in a cart.