Take the time at one of your pre-departure meetings to collect tip money from everyone in your group. This is a fail safe way to make sure that you will have the tip covered before arriving on tour.
That breaks down to:
$6 per day per traveler for the Tour Director
$3 per day per traveler for the Bus Driver
$1 per day per traveler to cover local guides, and possible bus transfers to the airport.
I always collect the tip amount in the US Dollar from my groups, and ask them to provide their individual amount in cash (to make my life a little easier).
On tour, I like to tip in the local currency. This is not required, and many group leaders will tip in the USD. It is personal preference, as I assume that the Tour Director and Bus Drivers probably appreciate receiving their own currency. This means that I will exchange the currency before my tour. I realize that comes with fees, and sometimes, an unfavorable exchange rate. Again, exchanging the currency is not required, just a little something extra I like to do.
Now that you have all of the tip money, you have a couple of options for how you want to actually handle the cash over seas. Here are the two most common methods for handling all that tip money while on tour:
1. Carry all the cash with you, and lock it up in the hotel safe. This is what I do. It makes me a nervous wreck to carry so much money with me on tour. I purchased one of those money waist belts, and I strap it to my body! I divvy out the money in small envelopes (for the Tour Director, Bus Drivers, and Local Guides) before I leave, and I like to keep it that way until I'm on tour. You can also split the money up between trusted adults on your tour, if that makes you feel better. I have even heard of some Group Leaders, giving the Tour Director 1/2 of the tip upon arrival (so that they don't have to carry it around for the duration of the tour), and then paying the rest on the last day of the tour.
2. Deposit the money, and then withdraw from the ATM while on tour. While this method is safer, you will need to double check with your bank that you will have ATM availability, and that you will be able to withdraw a large amount, and it not be mistaken for fraud. My daily limit at the ATM is around $250, so this method wouldn't work for me.
In the end, you need to do what works best for you. Talk with your Tour Consultant if you have concerns about tipping.