It's always best to obtain pre-authorization from the carrier for any expenses and to have your PNR noted or an email from the authorizer. This is especially true in the case of uncommon expenses, e.g. club rentals.
Beyond that, a rule of thumb is to ask yourself what you would spend, if anything, if the expense were not reimbursed. Might you spend GBP 100 instead of GBP 240 on an outfit? Why? Because the carrier may not reimburse you at all, may deem your expenses unreasonable and only partially reimburse. At that point, collecting what you believe to be your due may force you to either forget it and move on or sue. At that point, if you spend GBP 240 on clothing and can't get it reimbursed, you are out the money and, if you ever see it again, it will be a long ways away.
Other tips include: 1) obtain a receipt for everything, no matter how small; 2) document why you spent the money (here, if you did not have prepaid non-refundable reservations and suddenly decided to golf, would it be reasonable to ask BA to reimburse); 3) keep expenses reasonable (as in commercially reasonable, not what you personally do).