The minimum viable stack
For any card worth more than $10: a penny sleeve, then a top-loader. The penny sleeve cushions the card and prevents micro-scratches from the rigid plastic of the top-loader. Skipping the penny sleeve is the most common mistake.
For grading submissions
A penny sleeve plus a semi-rigid (sometimes called a "card saver") is the standard grading submission stack. Most graders require semi-rigids and refuse top-loaders because the top-loader has to be cut open to remove the card, and the cutting process introduces risk.
Binder pages
Cardboard or PVC binder pages can chemically migrate over time and damage card surfaces. Ultra Pro, BCW, and Dragon Shield all make archival, non-PVC pages. Read the page packaging before buying. The diagnostic is whether the pages are marked 'archival safe' or 'PVC-free.' Cheap pages are not.
Humidity, light, and temperature
Vintage Pokémon cards are made from a softwood-pulp cardstock that absorbs ambient humidity. Long-term storage in a climate-controlled space. Under 50% relative humidity, away from direct sunlight, at room temperature. Preserves edges and surfaces. A safe deposit box is better than a basement; a closet on an interior wall is better than a window-facing shelf.
The over-protection trap
A card sealed in a sleeve, a top-loader, a card saver, a box, a binder, and a safe is not safer than a card sealed in a sleeve and a top-loader and stored well. Each layer of protection is also a moment when the card has to be touched. For an actively-tracked binder, simple is durable.