Managing

I am at work again, as you could probably guess by the fact that I am blogging (no, I still don't have internet access at home), and I have just discovered the roster for next month. I have been put down to cover for the manager yet again while he has two days off! The "senior" supervisor is gonna get p'd off again when he spots that! And, this was all after the manager came back from his suspension and immediately changed his computer password as "Too many people" (i.e. ME) "have access to his stuff!"
Yes, it all looks good on a CV that I have covered for the manager position, but every time I do him a favour like this, and like covering the receptionist's holidays (as I am doing next Friday) I lose money. If I do a normal overtime shift it would be 12 hours. When I cover reception it is 10 hours (with lunch being unpaid, so really 9 hours), at the same rate of pay as I get at the moment. When I cover the manager it is for only 10 hours, and even though it is at a higher rate I end up about £5 worse off, I know that it's not much, but I resent doing all these favours for him without actually getting any benefits back myself. Does that make me selfish or does that make me a mug?
At least tonight is a "short" shift (11 hours), and then I only have one more night shift before 3 days off! See, I can think positively sometimes!