Items have a particular drop chance depending on their rarity, and in some extreme cases, some items may have an extremely low drop rate.
As of right now, common items have a 10% drop chance, uncommon items have a 5% drop chance, and rare items have a 2.5% drop chance. All items but Blair follow these rules, Blair however has an initial table chance, which means there is only a 20% chance of Blair even being on the rare drop list. This makes Blair's drop chance 0.5%.
The following charts display the number of drops per item that Lp81 had encountered, some of these scenarios were tested for over 20 hours! Some of the charts also include hay and rocks. Please note that all of the charts are based on the assumption that the player will drag 500 items per hour. In order to see the charts in great detail, you may have to click on the chart image and click on More Info in the top right of the popped up box, then click on Full resolution to open the full sized image.
This chart contains all of the results obtained, for a more specific scenario/item please refer to the charts below this one. As we can see, Jester items drastically improve your chances of getting items, especially in the case of Blair.