According to the IRS (I'm assuming you're an American, please advise
if this is incorrect), you should be getting receipts from every
charity to whom you donate:
"You must keep records reflecting the amount of cash and noncash
contributions you make during the year. The types of records you must
keep depend on the amount of your contributions and whether they are
cash or property.
Note: A qualified organization must give you a written statement if it
receives a payment of over $75 from you, and your payment is partly a
contribution and partly a payment for goods or services. Keep the
written statement for your records."
"For a cash contribution, the type of records you are required to keep
depends on whether the contribution is:
Less than $250, or
$250 or more
In figuring whether your contribution is $250 or more, do not combine
separate contributions. Each payment is a separate contribution."
"For each cash contribution under $250, you must keep one of the following:
A cancelled check or a legible and readable account statement that
contains the amount of the contribution, the date posted (or
transaction date if the contribution was charged to a credit card),
and to whom paid.
A receipt (or a letter or other written communication) from the
qualified organization that contains the name of the organization, the
date of the contribution, and the amount of the contribution.
Other reliable written records that provide the name of the qualified
organization, the date, and amount of the contribution. Your records
are generally considered reliable if they were made at or near the
time of the contribution and were maintained by you. If, in the case
of small donations, you have a button, emblem, or other token
regularly given to taxpayers making small cash contributions, these
items may satisfy your recordkeeping requirements for the small
For additional information on recordkeeping requirements, refer to
Publication 526, Charitable Contributions. Publication 526
[http://www.irs.gov/pub/irs-pdf/p526.pdf] is available for download or
you may request a copy by calling 1-800-829-3676."
If you have not got some kind of records to back up your charitable
contributions, then you aren't allowed to take them, per "You are not
allowed to deduct your charitable contributions because you did not
satisfy the acknowledgement and recordkeeping requirements."
These pages are successive steps in the Charitable Contributions Tax
Trail from the US IRS
found this by going to the IRS and selecting information for
individuals, then a search for "receipts and deductions".
Please let me know if I can clarify this answer further!