The mekubalim say that on erev succos we should give tzedaka. This makes sense because on the first night we invite Avraham Avinu into our Succah and how will he come in if we haven't first fulfilled his middah of צדקה. [Also, we remember the Pre-Yom-Kippur discussions of the tikkun habris accomplished on Yom Kippur. When Avraham sees that we have fixed "his" bris he wants to come right in and join us.]
A hint to this.....
A kosher succah is minimally 7 by 7 tfachim. All together - 49 square tfachim. Two of the walls must be 10 tfachim high. Multiply these 10 tfachim by 7 two times and you get 140 [70 square tfachim per wall]. We are at 189. Then the third wall must be a tefach wide and ten tfachim high - another square 10 tfachim. 189+10=199.
199 just happens to be the gematria of צדקה.
:-)
עפ"י הספר להורות נתן והספר אוצרותיהם של צדיקים