Request another one ASAP. When I went to MEPS, my recruiter told me that I could bring my passport and driver's license instead of my social security card which turned out to be wrong. Luckily, my family lives 20 minutes from MEPS so I was allowed to wait for my dad to come and bring it. But they were going to send me home and reschedule without it. So even if you can get by without it on your application (which I doubt), make sure to get ahold of it soon.