The carb-up foods don't have to be "sugary junk", but early in the carb up you DO want to eat foods that are high on the glycemic index. Sugar/glucose is VERY high-GI so I choose to use it. You don't HAVE to ... Other healthy examples of High-GI foods are:

Mashed potatoes
Rice cakes
Cold breakfast cereals (most of them anyway)
Cream of Wheat
Pasta
Jam/Jellies
Honey

Also, bananas, grapes, apple juice, grape juice, and carrots but these should be used in moderation due to the liver glycogen issue.