To be even more precise, let's brown townyze the contents of a said file.
>CLIENT
inventory1 brickMusicData
inventory5 brickMouseData
inventory9 brickDisplay6Data
currInvSlot -1
inventory0 brick1x1RampFFData
inventory2 brickHandle1x1fData
inventory6 brickBlockStationData
instantUseData brickDisplay6Data
currInv -1
inventory3 brickHandle1x1x2Data
inventory7 brickAshtrayData
score 98
inventory4 brickHandle1x1Data
inventory8 brick5xMusicData
>PLAYER
datablock PlayerLobby
transformPerMap -60.3706 -155.611 0.00545979 0 0 1.00001 0.0814682
velocity 0 0 0
damagePercent 0
scale 1 1 1
tool1 WrenchItem
tool2 PrintGun
currTool 1
tool3 0
tool4 0
tool0 hammerItem
It seems to save what bricks you have in your inventory, which brick you had selected and score for the client, and regarding the player, the playertype, location, even current velocity, health, scale of the player, all weapons and which weapon you had in your inventory.
That, in theory at least. I didn't really see it do any good job at loading those values.