Everything in Master Collection Vol.2

The store page blurbs it in one line, but here's the full list — what you actually get for $49.99, straight from KONAMI's official release notes and the Steam page.

Three games

• Metal Gear Solid 4: Guns of the Patriots — the 2008 PS3 classic, in its first release outside the PlayStation 3. Enhanced visuals, achievements, trading cards, cloud saves, adjustable difficulty, controller support.
• Metal Gear Solid: Peace Walker (HD Collection version) — the HD build previously only on PS3 and Xbox 360. Single-player campaign plus online co-op for up to 6 players.
• Metal Gear: Ghost Babel — the 2000 Game Boy Color spin-off, included as a purchase bonus. The series' first handheld outing, and a classic most modern Metal Gear fans have never played.

The digital extras

• METAL GEAR SOLID 4 Database — an in-game reference covering the lore from the original Metal Gear through MGS4.
• MGS4 Screenplay Book + Master Book — full in-game text, plus a story-and-character guide.
• Peace Walker Screenplay Book + Master Book — same treatment for the Big Boss story.
• Digital Soundtrack Vol.2 — the vocal themes and BGM that carried Snake's missions through the years, playable in a dedicated in-game sound player.

All of these open from the in-game Start Menu, per the Steam description. No separate launcher, no QR codes.

The Vol.1 save-data bonuses

Own anything in Master Collection Vol.1 on the same account and you get two unlockables in Vol.2, confirmed in KONAMI's official notes:

• MGS4: Gold Camouflage
• Peace Walker (HD): GOLD uniform

Both are earned by playing the respective Vol.2 games. Playing Vol.2 first and Vol.1 later still counts.