This is just my personal perspective for the most part, but I think a lot of the anxiety I feel stems from innate, primal survival instincts that have no real need anymore in my life position. For instance even though I could support myself and probably a small family on my current compensation, but I still feel the urge to get a raise. I still worry about my motorcycle getting stolen off the street even though it's a leisure vehicle and is a used, small bike that costs less than what I make in a week. Neither failing to get a good raise nor having my motorcycle stolen has any significant impact on my basic needs (heck, the latter would statistically improve it), but I think a primal urge to acquire and keep resources fueling my anxiety over these things.
These urges used to be necessary - the cave man that didn't worry about feeding himself and didn't worry about having his stuff stolen probably had a tougher time surviving - but I think the urges remain but there's no real outlet in many developed parts of the world.
As an addendum, I think a good way to mitigate this is to find things that satisfy these urges when possible, and be serenely introspective about the things you can't. When I stress out about material resource, I calculate how long I can live comfortably with no income and try to tangibly see hoe wide my safety net is (granted, this is not something that may result in reduced stress for everyone). But some things just need to be accepted as a part of myself. For instance when I feel the temptation to sleep with other women I just have to accept that this a part of an innate instinct to impregnate as many women as possible, instilled through hundreds of millennia of evolution in a society vastly different from the one I currently live in.