Adding this here as text.
The 2024 IRONMAN Rules have been published (wef 6 March) and the relevant section is:

5.01(m) Except as set forth below in Section 5.02(b) [actually IM may have wanted to refer to 5.03(b); below but it's not clear (5.02(b) refers to helmets)], additional equipment that has the effect of reducing wind resistance is prohibited during the bike segment of the Race (whether such equipment is worn under the athlete’s clothing, over the athlete’s
clothing, or is otherwise attached to the athlete's body or the athlete’s bike). This
includes, but is not limited to, (i) any bottles/hydration or any other insert located in
the front of an athlete’s race suit and (ii) any insert in an athlete’s calf sleeves; (DSQ)

5.03(b) Protective screens, fuselages, fairings, or any other devices or materials (including
duct tape) added or blended into the structure with the intent to reduce (or having
the effect of reducing) resistance to air penetration are prohibited. Aerodynamic
assemblies and protuberances on the head tube or elsewhere are prohibited; (DSQ)

This rule implies that temporary storage of a bottle in a pocket or down the front (see Sanders at Oceanside) will risk a DQ. And chucking outside a litter zone will mean DQ.

As for zippergate (off topic):
6.01(e) Uniforms with a front zipper may be unzipped to any length, provided, that (i) the
zipper should be connected at the bottom of the uniform at all times, and (ii) the
top of the uniform should cover the shoulders at all times; (30 or 60 Second Time
Penalty (as applicable), DSQ if not remedied promptly). The uniform should be fully
zipped when crossing the finish line;
Note that zipping up at the finish is a 'should' not a 'shall' and has no penalty attached
but IM have used 'should' when they mean 'shall' or 'is to be / are to be' on all this stuff.