Would a medicae-trained player be able to stack field sutures and a medi-kit to gain an extra bonus to tests, or should a skill test allow just a single tool?

For example, a player is suffering blood loss. A medic wants to know if she can use the field sutures (+30) and medi-kit (+10) to staunch blood loss at a +40 to her roll? Or should it only be a +30 from the sutures?

I generally allow stacking separate items, myself. For your example, it'd be combining field sutures with some kind of anti-coagulant out of the kit. Same process for cameoline cloak + stummer; one conceals your body, the other dampens your sound (stummers only last 20 minutes anyways). That said, if you had something like a full medical suite giving a +40, I wouldn't stack the medi-kit or field sutures; it'd be assumed those are already in the suite you're using.

A GM is to go with what he considers logical at the moment. I would permit field suture and medi kit since the field suture could be interpreted as close the blood flowing, while countersceptics, unguents and even some medicae gel could be used to make a proper a fast cicatrisation of the wound.

As far as I'm aware, there is no concept of "typed" bonuses like you would see in other systems, and generally it all adds up. The main limit is that it can only go up to +60 in bonuses.

As others though, the GM would have final say in this. That said, coming down on the players over a blood loss related medicae check is really not a good idea (although I guess 2nd edition has made it less terrifying than it was in 1st).

Depends, in the DH2, it's pretty sure you're charactier will die in a set period of time if he has no help in a short period of time, while previously taken points of fatigue will add up to his already dire state of health

Thanks for all the input everyone. I ended up telling my player that she can use both, and get both bonuses, based on the logic of using the sutures to close a wound, and various medicines/chemicals from the med-kit to slow the bleeding/stave off infection, what-have-you.