Just for clarification, by off the grid, do you mean simply alone (or with very limited grogs) and far from any town or do you also want to be mobile (like a wandering magus setting up his lab according to fluctuating auras ?) ?
Far away from civilisation and without much grog can be achieved relatively easily if you build up a good collection of tablets and/or minor magical item. With various Circle duration spell, you can easily set up ideal conditions to grow many ingredients (from animal or vegetal origin), regardless of where you are physically located. You only need to have with you a few seeds/pups/chicks to start accelerated growth.
Re or Cr Ig spell, possibly with Auram/Aquam requisit, with Circle duration will insure a glasshouse effect wherever you need it. Combined with a Circle of Accelerate growth and Blooming and you can grow anything that you have seeds/roots/fruits.
With a little bit of resources, you might consider crafting a pool of fertile soil of 10 paces diameter, one meter deep, circle by stone, magically hardened and enchanted with flying properties. Draw the required circle on the rim each time you need to grow something, speed up its growth, harvest, rinse a repeat for every item you needs, and you can even do it in a desert of stone since you are bringing the soil with you.
In this case, the magus can take time to carve into stone a proper circle around his "field" and it is unlikely that it will be disturbed. He can take all the time he needs since there is no rush and if he needs to recarve it from time to time, that's still okay, it is not like if the circle was imprisonning a demon.
You will need a few grogs with appropriate skills to turn the raw material into usable goods, but a good scores in Philosophae/Artes Liberales/Medicine, combined with the right Rego magic can also overcome that. With good Finesse and again the right spells, you won't even need Craft skill to turn skin into leather or parchment, reed into papyrus, extract salt from sea water and so on.
Similarly, a grog with Dousing virtue with a pendulum or a divining rod enchanted by a Rusticani with the right virtue can find almost anything as long as it is present in the area (various Intellego spell can do it as well).
I tried to limit myself to non-ritual based solution - the creation of some magical items can require virtus.
All in all, Mysanthropus the Lonely will need many spells, but of relatively low magnitude and a relatively broad set of skills (as already mentionned Artes Liberales, Philosophae, Area Lore (Medicine is only an option), probably with a good emphasize on Finesse (using Creo magic requires a good supply of virtus so is more Saga dependent).
It might be tricky to pull that off with a magus just out of Gauntelet, but achieveable within 10 years would be my guess: acquiring and developping non-hermetic skills is probably the limiting factor, and maybe he will have to developp a few specialty spells of low magnitude, but possibly not available from a labtext if too specific/unique.
Peregrinus the Lost will find additional challenges since he needs to be able to pack and unpack his whole sanctum, plus housing. He will need additional spells of higher magnitude and the ability to move many, many crates.
Depending on your reading of Scattering Like Light (HoH:S p 63), you can use various MuIm(Form) to temporarily change an object into his image (there was a few threads where similar spells were used to move people or even whole army, raising question about the passing of time, aging hunger and such), thus making is very easy to carry around since a book can contain all you need - just don't burn it.
Otherwise, if you find it too much of a strech Covenants has rules for movable lab.
A magical item with a boosted (larger range, faster move) variant of the Invisible Servant (maintaining concentration for safe transport) is a good investement.
What could be a bit more challenging is to keep contact with Redcaps for the ever-so-precious trade of labtext and books. If you don't offer comfortable housing and are hard to reach, they might visit you only once in a blue moon.
Of course, if you start talking about older magus, then most of these things become trivial: teleportation will allow them to go wherever they need to get what they want, and transport it back.