Back up the truck

In the context of general equities, "Prepare for a very large buyer."

Informal; to take or recommend an extremely bullish position, especially with a large investment. For example, if one believes that Stock A will soon rise in price, one may back up the truck on that stock by investing a particularly large amount of money in a long position. Backing up the truck implies a great deal of confidence in the proposed investment. The term derives from the image of a long-haul truck backing up to a warehouse to load up.