Hi MiniPigs,
That's a very broad question!
But since you mention "British and Afghan" I will assume you are mostly interested in those campaigns, and give you info focused on them. My overall qualifier is that there is limited number of such figures available, so in terms of "best sculpts and products" at least IMHO it's more a question of "Does anyone even make this?" as a bespoke sculpt, rather than a figure you will have to convert yourself.
You're probably familiar with Empress Miniatures, which makes an awesome range of 28mm 1879 Anglo-Zulu War figures. They don't have any bespoke Royal Engineers figures but they have several great character and officer packs, and a ton of British Infantry, which can be combined and converted into useful British Sapper or Pioneer types.
Also, many of the figures I'll discuss below really belong to the slightly earlier period of say 1878-1890, but it's a question of how much of a stickler for absolute accuracy in uniforms, equipment, and weapons detail you are.
That being said, there are some nice choices available…
The Australian company EUREKA MINIATURES makes "Sikh Pioneers c.1880" and "Punjabi Pioneers c.1880," as seen here as raw lead and also my own painted version:
Eureka figures are on the smaller side of 28mm, similar to old school Wargames Foundry, but I use them in the same army as slightly larger Perrys, Empress, and even larger Artizan Designs.
Here's a LINK to the "Colonials" page on their website, which includes both packs:
link
The only other later 19th Century Afghan War/NWF "pioneer" or "sapper & miner" sculpts I know of were made by an old company named, appropriately enough, Pioneer, but sadly have not been available for maybe two decades. They were very nice but also old school "true 25mm."
In its original version the Wargames Foundry Zulu War range sculpted by the Perrys included British soldiers in shirtsleeves with open hands, who you could turn into RE sappers with relative ease. They are not currently available on their website but if you emailed to ask you might be able to get some. These are also on the much smaller end of 28mm scale.
Speaking of the Perrys, their hard plastic NWF/Sudan infantry could be similarly converted into RE types with relative ease, if you are up for the conversion work.
RE: Porters…
About 25 years after it was introduced, the Wargames Foundry Indian Mutiny range remains the best source I know of, at least for NWF and 19th Century Afghan War stuff:
If you are looking for African porters, in addition to the "Darkest Africa" ranges from various ranges there are some nice ones in the Eureka Colonial range.
For Indian/Afghan civilians, there are a couple of appropriate packs in the Foundry Indian Mutiny range. There is also a wide selection of useful Indian and Arab types, including women and children, in the 28mm Eureka "Civilians and Vignettes" range, listed here:
link
There is also one great pack of "Muslim Civilians" in the Perry Crusades range, as seen here --
-- and available here:
link
The Perrys also have a pack of Ottoman Civilians in their Napoleonic French in Egypt range which could be of use.
Some great choices for ambulances include the Foundry Indian Mutiny "Dhoolie" pack, seen here:
…and available here:
link
…and the Castaway Arts camel ambulance:
Available here:
link
Castaway Arts also has baggage mules, water mules, and pack camels on that "Baggage & Transport" catalogue page.
Other pack camels and pack mules are pretty easy to find from various manufacturers, including Foundry, Northstar, etc.
RE: tents and barricades… again, you can find them pretty easily via a Google search, but a few easily available and nice choices are the Renedra plastic tents range available here:
link
…and Empress has a wide range of accessories useful for barricades in both their Zulu War range and also in their "Builders Yard" here:
link
looks at a fast-assembly naval kit for the Age of Sail.
