Hello,
as I've been handling quite some travel refunds, and often stumbled upon the same issues, I'd like to briefly mention four important hints:
(1) Please do not send your requests to SPI on your own. Only send them to TDF's treasurer, who then will ask SPI if they can refund from the LibreOffice budget.
(2) If you drive by car, please keep invoices from the gas stations. While we do have a per-km-rule, at least when we ask SPI for refunds, invoices are needed.
(3) Please do not send in receipts for events you attend when nobody approved it so far. As per the board's decision, all expenses must be approved by one of the budget holders.
(4) As a general rule, TDF can only refund the cheapest fare possible, i.e. only regular hotels, usually between 3 and 4 stars, and only 2nd class fares. Notable exception to the latter one is if a trip by 1st class is cheaper. In those cases, however, refunds are only possible if you send in proof that at the time of booking (!) the higher class trip indeed was the cheapest one.
Sorry if I am nitpicking here, but chasing those issues usually suck up a fair amount of time. 
Thanks for making the life for our treasurers easier,
Florian