Medieval Soldier / Mercenary Messing Gear

[Kitsune]

I am using the modern term and I also understand there is likely almost infinite variation.
Still, I am trying to get a handle on the standard messing gear each soldier / mercenary might carry as far as messing (eating) gear?
Of specific importance is what material would they be made from?

[Broomstick]

Of prime importance would certainly be one's personal knife, carried by all members of society back then. Not the blunt-point dinner knife of today but a sharp, pointy thing more like a small dagger. It was used only to cut meat and vegetables, it peeled apples, speared chunks of food on the point for conveyance to the mouth, the point could be used to pick one's teeth, and really, it was more of an all-purpose pocketknife so it could also trim nails, cut string and twine, whittle wood... but everyone had one.

The blade, of course, would be made of metal. Most commonly iron, and it was probably used frequently enough to avoid rust with only minimal care. The handle could be wood, bone, ivory, metal... almost anything, really.

Forks weren't common (as I said, the point of the knife would serve) but a spoon was a likely addition to the mess kit. I'm not sure about plates, bowls, mugs, etc.

[LaCroix]

First of all, forget the word "standard" when talking about middle ages military gear. Everything was purchased by the person in question, and rarely provided centrally. Then you need to give us a year.

What Broomstick said about the knife is absolutely correct. Everyone carried an iron knife, always, everywhere. Some peasants even carried a hatchet, too, for their daily work. Wooden or iron spoons were also part of the daily kit.

While the knife was used for cutting, if necessary (most food was already pre-cut and served as stew) - most people would eat with their fingers, though, as "food is a gift from god, and not touching it would mean that it's not worth being touched by man". At least that's something they said in Italy (about 1005), about some prominent woman using a fork - only after 1500, forks became fasionable in more and more countries. They'd normally just pour it into their hollowed-out bread loaf, use the spoon to eat what they could, and then tear up and eat the soaked bread. If they didn't have proper loaves, a bowl would be used. Usually, a soldier would carry a wooden bowl for that purpose.

A mug/cup/goblet for drinking (wood or tin, or whatever the man would buy himself - some mercenaries went all out on their personal gear...), eventually. If bottles were at hand, people would pass them around, and most soldiers would simply drink out of their canteens or waterskins to make sure they got emptied and refilled in regular intervals to not become stale. Mostly beer and wine - water was rarely used during a campaign out of fear of dysentery.

[Spoonist]

I am using the modern term and I also understand there is likely almost infinite variation.
Still, I am trying to get a handle on the standard messing gear each soldier / mercenary might carry as far as messing (eating) gear?
Of specific importance is what material would they be made from?

Could you be a little more specific?
Early , High or Late middle ages would help.
Like which country/culture/etc.
Since you didn't mention anything about region, I'm guessing europe since that is usually what we talk about when mentioning the middle ages, but europe is huge and usually at the end had overseas territories to boot.
The result would be very different if you are talking about norsemen in byzans, landsknecht in Denmark or eastern roman auxiliary.
Large company, individuals etc also matters. Footmen or riders, etc etc etc.

Common items, in falling order.
1) Wooden bowl(s) - almost universal. In some regions where wood was scarce this would be clay bowl. But clay isn't good for travelling.
2) Eating knife - almost universal. Size and material changing depending on culture and era. Please note that unlike stated above, not all would be of iron. Lesser metals was much more common during Early and High in lots of regions. In some parts/eras this would even be wooden knives.
3) Spoonlike utensil - often in the form of a smaller bowl with a hole in the side, but also full ones with a shaft and detailed carving etc. Same as above for clay substituting wood in some locations.
4) Water skin - almost universal. The contents though would preferably be somewhat alcoholic for obvious reasons.
5) Firestarter - Early, this would usually be an ember carrying bone container, Late you'd see all kinds of gear. This would of course also include kindle.
6) Salt container - usually a wooden flask. If you are going to be marching a lot, you need your own salt supply. Some regions put seasoning directly in the salt for a combined effect.
7) Oil skin - especially in the medditeranean region.
small hatchet - in north europe, during some eras/cultures it was more common to have a metal hatchet than a metal knife.

Couple of common things if you were supposed to cook as well. Sometimes/usually carried by the followers and not the mercenary.
1) Cooking pot - sometimes each had one, sometimes a shared of better quality, usually a combo of thos, having a wooden/clay pot for own use, and iron/bronze for shared use.
2) pottery - and lots of it
3) Barrels - everywhere you'd see casks and barrels. There are lots and lots of smaller ones for daily use.
4) vinegar - loads of it for obvious reasons.
5) pestle - many food sources needs grinding to be cooked/eaten. So carrying a pestle/cudgeon was very common. The mortar is much later and only among followers.
6) fire wood - obvious
7) wooden shovel - almost universal in camps, not so much on individuals. usually goes on the pack animal/oxen cart.

[Kitsune]

Bad use of the word "standard"
What I mean is that socially there must be things that are common not as in being issued.

[biostem]

I'd imagine that some sort of cloak or simple overcoat would be common - probably oiled to protect against water. This would also likely serve as a blanket. I would also imagine that people who were frequently on the go would either carry some bits to make snare or trap, and probably some smoked, dried, or salted meat. I would expect some other odds and ends, like a bone or metal needle and sinew or thread/string, to be common - for patching worn clothing or possibly to stitch a wound.