Closing up the bottom.
With the bottom row of vertices still selected.
Hit E to Extrude. Edges.
Hit Esc (escape)
Hit S to scale inward
Hold Ctrl and mouse in fives. X 0.5000 Y 0.5000 Z 0.5000. enter

Hit E to Extrude. Edges.
Hit Esc (escape)
Hit S to scale inward
Hit 0.
Hit enter.
See image.

Need to add some materal to the jar.
Time to make the cookie jar glass. You can color the cookie jar any way you want. Here is a quick way to make it glass.
Hit (toggle) Tab to go into Object mode.
If you haven't done it yet hit the Set Smooth button on the links and materials tab.
Right click the jar to select it.
Hit F9 on the keyboard.
From the link and material menu.
Click New for a new material.
Hit F5
Change the default material name to glass.
Move all three color sliders to the right for all white.
Now set the shaders tab to the settings in the image.
Set Mirror Transp tab to the settings in the image as well.
I combined the two images