This is what I have generally received for travel:
- Accomodations (up to a set limit per day which is told to you in advance) will require a receipt
- Food (can be a set limit per day or per meal - does not usually include alcohol except for sales people) may or may not require a receipt, check with your employer
- Long distance Travel - airfare generally paid in advance by the company, do not pay for this yourself and get reimbursed later!
- Local travel during the trip - either a rental car or taxi/bus fares. Note that local travel generally does not include paying for a taxi to go out at night for entertainment purposes or mileage for the rental car other than to and from teh place of work and the airport (unless you get unlimited mileage which is preferable). Includes the cost of gas. Receipts almost certainly needed.
- Fees - things like parking, tolls etc. but again only those associated with travel to the airport or to and from work or work requirements. If you choose to visit somewhere on your day off, then the toll to get there is generally not covered. Receipts might be needed unless you have a policy of receipts not being needed under a certain amount. Fees for overweight luggage will generally only be covered if you are taking heavy stuff specifically for work.
I have never traveled anywhere that toiletries and calls home were reimbursed. However, it can't hurt to ask.
In general, if the cost is required to get you to the work place or to maintain you in the other country, it will be covered. Entertainment costs are generally not covered unless you are entertaining clients.
One real caveat of the 3-6 week trip is that you want a cash advance for expenses or a corporate credit card. Otherwise, you could easily cost yourself a ton of money using your own cards or cash. Especially if the bills will come in (as in the 6 week trip) before you get reimbursed. So when you talk to your boss, talk about how these expenses will be paid for at the time of the expense. And make sure to get and keep a receipt for everything.
You should also be able to get local currency from an ATM. Keep good track of exchange rates and fees involved. If you are there for that length of time, you should also consider bringing an unlocked cell phone and purchase a local sim card with low rates to call and text home. In some cases these services can be extended to smartphones. Access to services such as Skype can be quite useful for contact with the office, friends and family.
If you run out of cash or have difficulties it is fairly easy for someone at home to send you money via Moneygram, Western Union or an equivalent service. The transfer can be completed in minutes and picked up at many locations. This is particularly easy in a remittance based economy like the Phillipines. Keep track of fees and exchange rates for such transactions.