4

The number 4 was the only number clearly visible on the die (for playing Mousetrap).

Locke mentions being on the island for 4 weeks now, while talking to Boone.

Locke    I know it sounds crazy. 4 weeks ago I wouldn't have believed it myself. But you and I are here for a reason. There's something that we were meant to find - something that's going to help us get into the hatch. I know it. But we've got to keep going.

Locke tells Boone that he was paralyzed for 4 years. 

Locke    I was in a wheelchair.
Boone    What?
Locke    Paralyzed for 4 years. The plane - our plane - I was in that chair when we took off. But not after we crashed.

8

Locke tells Emily that regulation footballs can be found on aisle 8. 

Emily    Yes, um, could you tell me where the footballs are?
Locke    Aisle 8 for regulation, aisle 15 for nerf.

There were 8 bags of heroin in the statuette that Boone threw to Locke.

The Nigerian drug smuggling "priest" was dead 2-10 years, according to Locke, a difference of 8.

15

Locke tells Emily that nerf footballs are found in aisle 15 at the ToyZone. 

Emily    Yes, um, could you tell me where the footballs are?
Locke    Aisle 8 for regulation, aisle 15 for nerf.

Locke's mother Emily was born 10-15-1940.

16

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23

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42

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All

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108

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815

815 in Chinese Letters on Boone's t-shirt.

Locke, while working in the toy store, told his "mother" that the regulation footballs were in aisle 8 and the nerf footballs: aisle 15.

Boone repeats over the radio that they are survivors of flight 815.

Boone    Hello. We're survivors of the crash of Oceanic flight 815, please copy.
Locke [overlapping]    Boone, get out!
Radio Voice    Hello. We're the survivors of Oceanic flight 815(?).