When my player-character arrives in 2050, she will see that her city has reverted back to the agricultural industry. Many years ago, my city was a small farming community. Also, I have researched what can be grown in this area: Cotton, peanuts, soybeans, grains (corn, wheat and oats), yams, spinach, cabbage and pecan trees. The game master says alcohol is also made.
I'm assuming that by "rebuilding civilization" you mean increase the technology level above its current in-game level. What aspect of technology? Medicine, power, weapons...? "All of the above" would be a pretty difficult task using stuff from a backpack.
This might help, though:
http://wtfoodge.com/lets-say-youve-gone-back-in-time/-Blast