The section of the British Triathlon Competition Rules that is most pertinent to transition is section 7.1.c, and detailed below:
7. TRANSITION AREA CONDUCT:
7.1 General Rules:
a.) All competitors must have their helmet securely fastened from the time they remove their bike from the rack before the start of the bike leg, until after they have placed their bike on the rack after the finish of the bike leg;
b.) Competitors must use only their designated bike rack and must rack their bike:
(i) For a traditional bike rack, the bike must be racked in an upright position. Bike must be racked in a way that does not block or interfere with the progress of another competitor.
(ii) In case of an individual bike rack, the bike must be racked facing out from the direction of the number.
c.) Competitors should only bring into transition what is required. Boxes may be provided by the Event Organiser, any other boxes used to bring equipment into transition should be removed. A small soft-sided bag such as a rucksack may be used and remain in transition, though it must not impede the progress of another competitor.
(i) Competitors must place within 0.5m of their racking position in transition, or within the width of the bike handlebars, all equipment to be used at a later stage in the event.
(ii) All equipment already used must be deposited in that area.
(iii) Only equipment to be used during the competition can be left in transition.
(iv) All other belongings and equipment outside the above rules are to be removed before race start;
d) If a competitor wishes to use the same shoes in a duathlon for the second run these do not have to be place in the box (where provided by the Event Organiser) or the competitor’s bag. However, only one pair of running shoes may be on the floor at any time during the race, and must be located within the competitor’s transition area.
e) Bike shoes, glasses, helmet,and other bike equipment or clothing required for the cycle segment can be placed on the bike;
f) Competitors must not impede the progress of other competitors in the Transition Area;
g) Competitors must not interfere with another competitor's equipment in the Transition Area;
h) Cycling is not permitted inside the Transition Area. Competitors must mount their bicycles after the mount line by having one complete foot contact with the ground after the mount line. Competitors must dismount their bicycles before the dismount line by having one complete foot contact with the ground before the dismount line. While in the transition area (before the mount line and after the dismount line) the bike can be pushed only by the competitor’s hands. If during the mount or dismount manoeuvre, the competitor loses their shoe(s) or other equipment, they will be collected by the Technical Officials or marshals and no penalty will be applied. Mount and dismount lines are part of the transition area;
i) Nudity or indecent exposure is forbidden;
j) Competitors must not stop in the flow zones of the Transition Area;
k) Marking positions in the Transition Area is forbidden. Marks and objects (such as balloons or chalk) used for marking purposes are not permitted and will be removed and the competitors will not be notified. Wetsuits or other items of clothing hung over racking is classed as marking;
l) The helmet strap must remain unfastened in the Transition Area while the competitor is completing the first segment;
m) Helpers, friends or family members are not permitted in transition areas.
n) Mobile telephones canbebroughtintotransitionbutmaynotbeusedwhilstthetransitionareaislive.
o) Pets must not be brought in to transition at any time by any person.
p) Where using bike lights would improve competitor safety, these are permitted.
As you can see from the above belongings must be within 0.5m of their position, or within the width of the bike handlebars which make KitBrix the perfect solution as 1,2 or 3 but we would always recommend using 2 bags for your event as 40l is more than enough space for what you need.