That’s absolutely true. Military would rarely if ever use anything except powder food and lead, from the enemy, it would only be rare, but possible for a civilian.
One needs think how would a person have got x
There is a very long documented history of soldiers scrounging for whatever they could use, and the use of captured military and civilian items. (Should I mention southerners during the ACW by way of one of the best known periods when southern soldiers sometimes wore so much Federal uniform items and equipment they were mistaken for Federals by other southern units?)
The visual media of the 18th century is limited to artists renderings, some of them made years or even decades after events happened. The accuracy of those renderings or paintings are not always considered accurate. That leaves us with having to consider written documentation, and there are indications that yes, captured items were used (or can be documented for specific time periods). Any use of "captured" items should be used, only with documentation that shows time/place instead of re-enacting and living historians do....for the entire war.
The light companies of the first battalion of the 60th Foot in 1758/9 swapped out their Besses for captured Charlevilles. Because they were not regimental/Crown property, they were permitted to cut them down so they be used as improvised fusils that were lighter to carry, easier to handle in dense woodlands and in potential close combat situations that arise when these companies were used as skirmishing and scouting elements. The light companies also heavily modified their issue regimental by cutting them down, removing "bulk" to the point that a regimental started to resemble a sleeved waistcoat.
Roger's Rangers were issued a uniform, however, the ranger units are also known to have modified whatever they had, in order to fit their own needs. Captured items of all sorts were used, including Indian made items (snow shoes) and mocs and/or bare feet were preferred because any footprints left behind and seen by Indians or French were not as easily identified as a shod foot being European, not Indian.
The French were notoriously short on script and coinage to use for paying troops. If there was hard currency available in the form of silver or gold coins, what monarch's head was on it was less important than the type of metal and how much it weighted.
On campaigns, leather footwear could wear out fast, and replacing shoes on the frontier or in your opponents territory, taking the shoes or mocs off a dead man or prisoners feet wouldn't have raised any eyebrows. Add to that, the long established tradition of searching prisoners for valuables and looting the dead.
In winter, soldiers in the field have often worn as many layers of clothing as they could get to fend off the worst of it. Captured winter-time clothing worn as layers under the outer and visible uniform. Shirts, waistcoats (depending on color, and overdyed if possible) might even be used in fairer weather.
SH....check out Track of the Wolf's fancy combination French musket tool, with ball puller, knapping hammer and screw-driver combination, but without the kitchen sink. It's patterned after one found at Louisbourg and is a period FRENCH item for use with a Charleville.
Instead of doing the ever-popular thing of "British" during the F&I Period, I'd suggest checking out French units (they are probably very rare out west where you are!). You might want to consider what aspects of the period appeal to you most. Some units focus on the military aspect, others place importance on camp life rather than a hard-core military impression so it can be a family centered unit instead. Then there are shades in-between.