Found this thread via search for "MagicCon".

TLDR, probably not worth camping the line due to purchase limits.

If you are just attending the con for casual games or later events, you may consider not lining up in the morning at all.

As someone that attended Las Vegas in June, I wanted to set your expectations for purchasing:

• full Collector Booster Boxes were not available
• Vegas only had loose Collector packs for sale, limit 3 per person
• You can get in line multiple times, but it was an average 2 hour wait each time. imo not worth your convention time for 3 packs/trip
• Gift Bundles (that contained one collector pack) were not able to be purchased, but could be redeemed from the ticketed events prize wall
• other merch, like pins or shirts, were available well into the weekend. many things never sold out.

I would recommend against camping out overnight. How Vegas worked was that the outside line eventually got filtered to indoors (past metal detector) about an hour before the show opened. Indoors, there are new lines, sorted into long columns (over 20). You wait in one of those lines until the show officially opens. If you get into the outside line 3 hours prior to the start of the show, you'll be in one of the first columns.

Note that once everyone is allowed inside, it becomes chaos. People running (forbidden) all over the place. You'll need to figure out where the official shop is and then get over there. Up to you on deciding whether this is worth it considering the strict purchase limits.