I really freaking love this game. High score is 4120.
The cute elevator music, the items you have to pack that get more insane, and SALMAGEDDON is exactly the type of thing the world needs.
I think instead of just an endless mode, a "story mode" where you work for various companies and have a boss that occasionally comments on your work, which could be fun. Each level, you can change, add and remove more elements of game play. Some levels you have to pack specific things in specific boxes, others only have tiny packages. Some levels you have more than just 3 items to choose from, or some that start with 6 but you get less items as you go. In another, you have full boxes that you have to empty in other ones.
Final level in story mode is obviously the north pole, where you work for Santa. And everytime you do a good job, he says something like "the kids are gonna LOVE that!" even if you just packed a bunch of salmon and an uzi.
Speaking of doing well, I think ti could be cool to add a multiplier of your score if you perfectly fill multiple boxes in a row. More incentive to fill the boxes carefully and well, and chase higher scores. Maybe a little "perfect!" can pop up when you do so as well.
Also, make the score count clearer. And make it clearer when you get negative points. Like, have a small buzz sound maybe, or the points you get deducted show up in a fun arcade-y, red font.
Overall, I really loved this. Hope you keep working on this game and release a full version! And let me know when you do :D