Two main ones:
* working from home rather than office when not travelling to client site. Means I have zero commuting time, can be somewhat flexible about hours, have my own lunch at home, work in my own environment, avoid some office politics. The time saving, work and personal flexibility & productivity benefits are great. I would NOT want to return to going to office every day (but ever man has his price...). Pure financial benefit isn't much compared to when living within walking distance to office.
* Pension contributions. By paying in a lot more than the standard to get the employer matching, I save so much income tax (and get half of the employer's NI savings, which is just an income tax by another name for those not in UK) that my total take home pay and pension contributions are £500 a month more, and all I had to do was fill in a simple form (though yes, I am reducing the flexibility of my savings a bit by having a higher proportion in a pension I can't access for another 20 years or so).
One mid size one:
* refunds from travel delays from work travel. When travelling every week, every few weeks a train is significantly delayed and I can claim compensation (while still claiming the original ticket cost as expenses - at time of claiming expense I do not know if I will actually get the ticket compensation, and the delays mean I am using my personal time for work travel). Does mean the delays have cost my time, but typically worth £500 or more per year.
Smaller things:
* Company offers access to a rewards scheme, most of it is just 5% or 10% discount on shopping in department stores etc., not very exciting if you are not generally a spendy person. However, it does offer 5% off supermarket shopping, so is worth a few £ a month for no effort.
* When travelling for work have work expenses so use cash back credit card and get some points too, no big numbers like in the US but at 0.5% cash back and same in points is perhaps worth £20 a month, again for no effort (have to pay and reclaim my expenses anyway).
* Travelling for work means I get free meals, so save food costs, must be worth at least £20 a month again. Also means I get meals out and drinks so feel less inclined to buy these myself.