The ornamental design for a self-heating container, as shown and described.
FIG. 1 is a front and bottom perspective view of the self-heating container;
FIG. 2 is a front elevation view thereof, a rear elevation view, a right side elevation view, and a left side elevation view being a mirror image;
FIG. 3 is a top plan view thereof;
FIG. 4 is a bottom plan view thereof; and,
FIG. 5 is a cross-sectional view thereof, taken about the line 5-5 in FIG. 2.
The broken lines in the drawings represent unclaimed portions of the self-heating container, which are included for the purpose of illustrating unclaimed environment only, and form no part of the claimed design.