Making your laptop unreachable..

Get piece of paper and pencil is the ONLY solution to your issue. Let me explain.

It is a known fact that if you use specialized EMP detecting equipment, due to the variations in the bit values that the 'pulses' can be measured to extract what keys your actually using, which back on CRTs was even worse as you could scan and pick up the electrical signal of the video and create a 'ghost' image to see what they were seeing on the screen. All this done from a van parked across the street from your office / house.

Further it is a known fact that you can bounce a laser off the glass of your office/house and record every sound made in your house, inclusive the different sound of each keystroke, to again reinterpret into the actual words your typing on the screen when run through a logic system. For example keys E and R close together 'sound alike' but the word detected is THRY, doesn't make sense so we estimate the word was actually THEY.

Both cases AND MORE have nothing to do with Wifi/etc. but simple ELECTRONIC TYPYING (yes this includes electronic typewriters and was a common set of tools used by Spy and CORPORATE SPY agencies).

Now the ONLY sole way to have a "laptop to type up and store information.... 100% guarantee that not a single soul can extract those files without direct physical access to the computer " is to have the Government or High end Corporate budget because what the ways are extreme and tried and true tested (Called COMSEC or COMputer SECurity). The solution requires multiple layer defenses to protect the objective to attain the goal. The first is physical, you need to ensure that (as mentioned) no method is detectable by any lasers, EMP detectors, etc. You would need to have a building with a office in the center, lead lined, with it's own filtered electrical system (specialized wrapping around the electrical cable so no one can see the pulses your electronically emanating by just 'using' the power). The central office would require a cypher lock, preferably a Retinal AND Handprint scanner (yes they do exist) to get to the ManTrap (these are used by jewelry stores and banks to gain entrance) with a armed security guard to be the final verification of access to the room, which only that guard can unlock, usually from behind a thick bullet proof seperate entrance /exit room that overlooks where your entering and exiting the mantrap to get to the room with the laptop.

These multiple physical layers also require the use of Concrete intertwined and wrapped with lead lining, so the reverberations and electronic pulses are not 'stored' / bounce off the rebar / steel of the structure. A extensive and specialized HVAC unit to provide clean A/C using positive negative pressurization would keep out the potential of tinfoil particles from flowing INTO the room causing the EMP dampening you provided and lack of vibration with the walls, now circumvented by the very air able to do that by reverberating off the particles.

Now you stopped your electrical input, output, EMP signature, physical access, vibration sensitivity, now the actual laptop itself. First off you would remove physically all 'cards, and disable (even if the card is missing) in both BIOS and OS level the device ports. Next you encrypt the drive fully in at least 512 level, current standard is 1024bit encryption (again very expensive and hard to get hold of) so anything stored or retrieved from the drive is hardware encrypted at all times, in addition you would need to run a Virtual OS session that as well is encrypted. The monitor and case of the laptop itself would need to be reworked, to include layers of lead over the CPU, GPU, wrapping the cabling in EMP wrapping (yes looks like tinfoil), add a layer to the entirety of the LCD itself , and of course over the HDD, and replace either with a optical keyboard or membrane to reduce the ability of the mechanical noise be detected.

All in all your price tag for a single specialized laptop that would be about 25lbs or so, specialized power cord/ source again filtered, the room, security, etc. is your typical $1-25M to achieve nearest (99.99%) probability of "guarantee that not a single soul can extract those files without direct physical access to the computer ".

As I said, the cheaper simpler solution, get a piece of paper and a pencil.