First you want a bottle that is made of the best material which is LDPE low density poly ethylene this means its a softer plastic that allows for easier heat transfer from warmer to urine and bottle to flesh. This plastic will be mostly clear and semi pliable,  as apposed to a hard white plastic. 

  The bottle should have a easy to read thermometer label  preferably with a 2 degree offset like the collection cups use for the most accurate temp.  

It is best to use a cap that  you can dispense without removing it which could result in you dropping it or leaving it behind  ( less things to mess with in such a situation ).

 
Warmers
Warmer should be the smallest hand warmer with longest activation time, not anything large that will result in excess tempt issues .
An adhesive tab or rubber band to secure warmer to bottle 
 
Powdered Synthetic Urine  
All Liquid Urine contains Biocides and or peroxides  which can pop a validation screen and leave sample flat and odorless .   
Powdered Synthetic    does not need to use biocides ,

 CARRY TIPS

To ensure accuracy, it is advisable to practice beforehand in order to determine the temperature after carrying the item for an hour and to confirm that it is securely positioned.
For a warm water-filled bottle, aim for a temperature range of 100 degrees Fahrenheit. To achieve this, you can briefly microwave the bottle few seconds, shake it, and then check the temperature. It is not advisable to use a warmer to heat the sample, as it would take a considerable amount of time.
The warmer is a insulating heat and body flesh regulates the temp pulling excess heat away from bottle .

 It is important to note that if the temperature exceeds the range of the thermometer, it will not be displayed. If bottle feels warms to hand its probably too warm as you can't really feel body temp unless hands are cold.

The sample should be added only when you are ready to conduct the test.


Pick up  extra hand warmers at walmart ( usually have 2 packs in check outs )  carry with water for an hour  and walk around to see how temp holds.  Carry both ways with and without  to observe if temp is issue . May not need them in summer however labs keep waiting groom cold as ice for this reason .
With a dry run you will have confidence and overcome any nervous issues.


For random testing scenarios,Carry the warm water and the vial separately.
Just remove cap from vial (put cap in pocket) then insert the vial into  bottle and secure cap  and shake.