Depends what I'm intending to do...
Looting: a bit of food and drink, a pistol (preferably an Sa 61), a big backpack, not much else except an extension cord to spawn a quad.
Looting a "busy zone" (like Balota): anything that takes a STANAG, preferably an M4 or Sanitised AR, otherwise see above. It'll be no time until you pick up all the attachments and ammo you need.
Mission: marksman rifle like a Mk1 EMR or an M14, AMS, suppressor.
Camping: large calibre long-range rifle like a Lynx or M107 and appropriate optics. Lots of food/drink.