You have a couple of options, but I generally set them up as material
resources in the resource sheet:
Resource: Hotel
Type: Material
Label: Night
Cost: USD 100
Then, in the Gantt Chart view, select a task, split the screen (Window >
Split), and in the bottom left, select your hotel, then under units, enter
"1/d". This will calculate one hotel night for each day of the task. If the
task gets pushed out, then more hotel nights will be calculated.
You can then calculate the cumulative cost for all hotel stays, and count
how many hotel stays, books, rental cars, etc. you have used.
Note this method works on material resources w/ low variability in cost,
i.e. you set up one resource for hotels and it is more or less the same
price. You can of course set up multiple resources for different hotel price
tiers, but that becomes a lot of work.
Or you can use the fixed cost field for the task. The only issue there is
that it doesn't itemize your costs, and you will need to add notes to the
task depicting where those fixed costs came from.....