The absolute minimum? That takes some thought - says he, who has a machinist’s toolbox full of exotic hardware, most of which is almost never disturbed.
For benchwork, my way, a 25-foot tape measure, small rafter square, tin snips, power drill (may be cordless) with crosspoint screwdriver bit(s) and a saber saw (for cookie-cutting plywood.) I build benchwork from steel studs.
For mounting roadbed to plywood subgrade - a large tube of latex caulk in a caulking gun (spread it out with the sample cards from your friendly credit card purveyor or similar source) and some weights (old phone books, dead batteries from cordless tools, 2-liter bottles of soda…)
For mounting plastic-tie track to roadbed - same as the above, but make sure you use either clear or grey caulk.
For prepping flex track - fine-toothed file, diagonal cutting pliers (or specialized rail-cutting tool,) hobby knife set with long (#11) and chisel-point blades.
Wiring - small-diameter drill bit (for the power drill) Soldering tool (enter “solder” in the forum search and get to read the pros and cons of guns vs/and/or irons. My personal choice is a heavy gun for layout wiring, and a needle-tipped iron for electronics and in-panel wiring.) Solder (60/40 or electronic solder, small-diameter with rosin core) and flux (NOT acid!) Nice to have - a low-cost multimeter.
The one tool you absolutely will NOT need is a hammer. Nails have no place in model railroad carpentry.
This assumes the use of plastic tie (sectional or flex) track and commercial turnouts, and does not include tools needed for assembly/maintenance/modification of rolling stock and structures.
Avoid cordless soldering tools and those ‘not available in stores’ super TV advertised deals. Most