I work in an expensive part of london. Nobody at work can afford to live locally, so we all have to watch the pennies.
Investigate less obvious ways to travel. By commuting to a station a half our walk away, I have halved my commuting costs. One colleague gets a coach and others cycle. Some colleagues who travel to mainline stations use boris biked instead of paying for travel cards for London.
Packed lunches are generally cheaper than canteens. We have a microwave and have soups, jacket potatoes and leftovers. We also bring in bread, cheese etc and make up fresh sandwiches.
Bring in a stash of tea, coffee and squash for drinks. Cheaper than Starbucks. i buy multi pack cans of coke which cost 40p each instead of 90p at the local shop.
Go for a walk at lunchtime instead of hitting the shops. Suggest lunch in the park to colleagues instead of eating in a cafe. That way you can eat your packed lunch.
If you don't have a kitchen available, take a hot flask, make up some sandwiches and crisps and find a quiet corner.
If you go for drinks after work, avoid buying rounds.
Don't feel obliged to donate to all the leaving presents etc, unless you want to. Nobody will know.
I buy stationary front the pound shop. If I attend a conference, I grab a few pens and post it's to use in the office.
Leave your money at home to avoid temptation. I'm not brave enough to do this myself, but the main thing is to avoid spending.
I've stopped buying daily newspapers. I grab a copy of the metro in the morning and evening standard in the evening. Both are free and i read them if I have a spare moment.
Most workplaces I know do that thing whereby you bring in cakes on your birthday. Bake one - it's cheaper and most people will be impressed.