Both branded items and local take on branded items are available in Kathmandu. It is totally possible to get everything and anything you will need for a trek here. A word of cautions about local products though: Being labeled North Face or Mountain Hardwear, as most local products are, doesn’t bless them with durability. However, there are good fakes and bad fakes and most are okay for the price. If you spend some time checking and rechecking the stuff especially the zippers and stitching, it will provide service for at least one trek. Or you could just stick to one of the branded outlets in Thamel.
However, bringing some stuff from home will save you time in Kathmandu and will also give you peace of mind. Also if you don’t know, the dress code for the mountains is layers. And avoid cotton inners at all costs.
If you are trekking on your own, you should carry the complete medical kit. However, if you are going through a trekking company, they will provide a medical kit. Chances of the kit containing moleskins, knee supports or anklets is almost zero though. Get these for yourself. You should also consider getting a list of the stuff they will provide and tallying it with the list we have provided.
Due to lax prescription requirements, most of the items are easier to get in Kathmandu.
More information can be found here:https://honeyguideapps.com/blog/an-independent-trekkers-guide-to-everest-base-camp
For more details go to What are the Permits Required for trekking to Mount Everest Base Camp under Everest Region for more details.
All treks inside the Annapurna Conservation Area will require these permits. These treks include the Annapurna Circuit, Annapurna Base Camp Trek, Mardi Himal Trek, Jomsom-Muktinath Trek, and Mohare Danda Trek.
For more details go to #How to get to Everest Base Camp? section of Everything about the Everest Base Camp Trek.